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 <div class="section" id="type-objects">
<h1>Type Objects<a class="headerlink" href="#type-objects" title="Permalink to this headline">¶</a></h1>
Perhaps one of the most important structures of the Python object system is the
structure that defines a new type: the <a class="reference internal" href="type.html#PyTypeObject" title="PyTypeObject"><tt class="xref c c-type docutils literal">PyTypeObject</tt></a> structure. Type
objects can be handled using any of the <tt class="xref c c-func docutils literal">PyObject_*()</tt> or
<tt class="xref c c-func docutils literal">PyType_*()</tt> functions, but do not offer much that&#8217;s interesting to most
Python applications. These objects are fundamental to how objects behave, so
they are very important to the interpreter itself and to any extension module
that implements new types.
Type objects are fairly large compared to most of the standard types. The reason
for the size is that each type object stores a large number of values, mostly C
function pointers, each of which implements a small part of the type&#8217;s
functionality. The fields of the type object are examined in detail in this
section. The fields will be described in the order in which they occur in the
structure.
Typedefs: unaryfunc, binaryfunc, ternaryfunc, inquiry, coercion, intargfunc,
intintargfunc, intobjargproc, intintobjargproc, objobjargproc, destructor,
freefunc, printfunc, getattrfunc, getattrofunc, setattrfunc, setattrofunc,
cmpfunc, reprfunc, hashfunc
The structure definition for <a class="reference internal" href="type.html#PyTypeObject" title="PyTypeObject"><tt class="xref c c-type docutils literal">PyTypeObject</tt></a> can be found in
<tt class="file docutils literal">Include/object.h</tt>. For convenience of reference, this repeats the
definition found there:
<div class="highlight-c"><div class="highlight"><pre>typedef struct _typeobject {
 PyObject_VAR_HEAD
 char *tp_name; /* For printing, in format &quot;&lt;module&gt;.&lt;name&gt;&quot; */
 int tp_basicsize, tp_itemsize; /* For allocation */

/* Methods to implement standard operations */

destructor tp_dealloc;
 printfunc tp_print;
 getattrfunc tp_getattr;
 setattrfunc tp_setattr;
 cmpfunc tp_compare;
 reprfunc tp_repr;

/* Method suites for standard classes */

PyNumberMethods *tp_as_number;
 PySequenceMethods *tp_as_sequence;
 PyMappingMethods *tp_as_mapping;

/* More standard operations (here for binary compatibility) */

hashfunc tp_hash;
 ternaryfunc tp_call;
 reprfunc tp_str;
 getattrofunc tp_getattro;
 setattrofunc tp_setattro;

/* Functions to access object as input/output buffer */
 PyBufferProcs *tp_as_buffer;

/* Flags to define presence of optional/expanded features */
 long tp_flags;

char *tp_doc; /* Documentation string */

/* Assigned meaning in release 2.0 */
 /* call function for all accessible objects */
 traverseproc tp_traverse;

/* delete references to contained objects */
 inquiry tp_clear;

/* Assigned meaning in release 2.1 */
 /* rich comparisons */
 richcmpfunc tp_richcompare;

/* weak reference enabler */
 long tp_weaklistoffset;

/* Added in release 2.2 */
 /* Iterators */
 getiterfunc tp_iter;
 iternextfunc tp_iternext;

/* Attribute descriptor and subclassing stuff */
 struct PyMethodDef *tp_methods;
 struct PyMemberDef *tp_members;
 struct PyGetSetDef *tp_getset;
 struct _typeobject *tp_base;
 PyObject *tp_dict;
 descrgetfunc tp_descr_get;
 descrsetfunc tp_descr_set;
 long tp_dictoffset;
 initproc tp_init;
 allocfunc tp_alloc;
 newfunc tp_new;
 freefunc tp_free; /* Low-level free-memory routine */
 inquiry tp_is_gc; /* For PyObject_IS_GC */
 PyObject *tp_bases;
 PyObject *tp_mro; /* method resolution order */
 PyObject *tp_cache;
 PyObject *tp_subclasses;
 PyObject *tp_weaklist;

} PyTypeObject;
</pre></div>
</div>
The type object structure extends the <a class="reference internal" href="structures.html#PyVarObject" title="PyVarObject"><tt class="xref c c-type docutils literal">PyVarObject</tt></a> structure. The
<tt class="xref py py-attr docutils literal">ob_size</tt> field is used for dynamic types (created by <tt class="xref py py-func docutils literal">type_new()</tt>,
usually called from a class statement). Note that <a class="reference internal" href="type.html#PyType_Type" title="PyType_Type"><tt class="xref c c-data docutils literal">PyType_Type</tt></a> (the
metatype) initializes <tt class="xref py py-attr docutils literal">tp_itemsize</tt>, which means that its instances (i.e.
type objects) must have the <tt class="xref py py-attr docutils literal">ob_size</tt> field.
<dl class="member">
<dt id="PyObject._ob_next">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyObject._ob_next</tt><a class="headerlink" href="#PyObject._ob_next" title="Permalink to this definition">¶</a></dt>
<dt id="PyObject._ob_prev">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyObject._ob_prev</tt><a class="headerlink" href="#PyObject._ob_prev" title="Permalink to this definition">¶</a></dt>
<dd>These fields are only present when the macro <tt class="docutils literal">Py_TRACE_REFS</tt> is defined.
Their initialization to NULL is taken care of by the <tt class="docutils literal">PyObject_HEAD_INIT</tt>
macro. For statically allocated objects, these fields always remain NULL.
For dynamically allocated objects, these two fields are used to link the object
into a doubly-linked list of all live objects on the heap. This could be used
for various debugging purposes; currently the only use is to print the objects
that are still alive at the end of a run when the environment variable
<a class="reference internal" href="../using/cmdline.html#envvar-PYTHONDUMPREFS"><tt class="xref std std-envvar docutils literal">PYTHONDUMPREFS</tt></a> is set.
These fields are not inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyObject.ob_refcnt">
Py_ssize_t <tt class="descname">PyObject.ob_refcnt</tt><a class="headerlink" href="#PyObject.ob_refcnt" title="Permalink to this definition">¶</a></dt>
<dd>This is the type object&#8217;s reference count, initialized to <tt class="docutils literal">1</tt> by the
<tt class="docutils literal">PyObject_HEAD_INIT</tt> macro. Note that for statically allocated type objects,
the type&#8217;s instances (objects whose <tt class="xref py py-attr docutils literal">ob_type</tt> points back to the type) do
not count as references. But for dynamically allocated type objects, the
instances do count as references.
This field is not inherited by subtypes.

Changed in version 2.5: This field used to be an <tt class="xref c c-type docutils literal">int</tt> type. This might require changes
in your code for properly supporting 64-bit systems.
</dd></dl>

<dl class="member">
<dt id="PyObject.ob_type">
<a class="reference internal" href="type.html#PyTypeObject" title="PyTypeObject">PyTypeObject</a>* <tt class="descname">PyObject.ob_type</tt><a class="headerlink" href="#PyObject.ob_type" title="Permalink to this definition">¶</a></dt>
<dd>This is the type&#8217;s type, in other words its metatype. It is initialized by the
argument to the <tt class="docutils literal">PyObject_HEAD_INIT</tt> macro, and its value should normally be
<tt class="docutils literal">&amp;PyType_Type</tt>. However, for dynamically loadable extension modules that must
be usable on Windows (at least), the compiler complains that this is not a valid
initializer. Therefore, the convention is to pass NULL to the
<tt class="docutils literal">PyObject_HEAD_INIT</tt> macro and to initialize this field explicitly at the
start of the module&#8217;s initialization function, before doing anything else. This
is typically done like this:
<div class="highlight-c"><div class="highlight"><pre>Foo_Type.ob_type = &amp;PyType_Type;
</pre></div>
</div>
This should be done before any instances of the type are created.
<a class="reference internal" href="type.html#PyType_Ready" title="PyType_Ready"><tt class="xref c c-func docutils literal">PyType_Ready()</tt></a> checks if <tt class="xref py py-attr docutils literal">ob_type</tt> is NULL, and if so,
initializes it: in Python 2.2, it is set to <tt class="docutils literal">&amp;PyType_Type</tt>; in Python 2.2.1
and later it is initialized to the <tt class="xref py py-attr docutils literal">ob_type</tt> field of the base class.
<a class="reference internal" href="type.html#PyType_Ready" title="PyType_Ready"><tt class="xref c c-func docutils literal">PyType_Ready()</tt></a> will not change this field if it is non-zero.
In Python 2.2, this field is not inherited by subtypes. In 2.2.1, and in 2.3
and beyond, it is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyVarObject.ob_size">
Py_ssize_t <tt class="descname">PyVarObject.ob_size</tt><a class="headerlink" href="#PyVarObject.ob_size" title="Permalink to this definition">¶</a></dt>
<dd>For statically allocated type objects, this should be initialized to zero. For
dynamically allocated type objects, this field has a special internal meaning.
This field is not inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_name">
char* <tt class="descname">PyTypeObject.tp_name</tt><a class="headerlink" href="#PyTypeObject.tp_name" title="Permalink to this definition">¶</a></dt>
<dd>Pointer to a NUL-terminated string containing the name of the type. For types
that are accessible as module globals, the string should be the full module
name, followed by a dot, followed by the type name; for built-in types, it
should be just the type name. If the module is a submodule of a package, the
full package name is part of the full module name. For example, a type named
<tt class="xref py py-class docutils literal">T</tt> defined in module <tt class="xref py py-mod docutils literal">M</tt> in subpackage <tt class="xref py py-mod docutils literal">Q</tt> in package <tt class="xref py py-mod docutils literal">P</tt>
should have the <tt class="xref py py-attr docutils literal">tp_name</tt> initializer <tt class="docutils literal">&quot;P.Q.M.T&quot;</tt>.
For dynamically allocated type objects, this should just be the type name, and
the module name explicitly stored in the type dict as the value for key
<tt class="docutils literal">'__module__'</tt>.
For statically allocated type objects, the tp_name field should contain a dot.
Everything before the last dot is made accessible as the <tt class="xref py py-attr docutils literal">__module__</tt>
attribute, and everything after the last dot is made accessible as the
<tt class="xref py py-attr docutils literal">__name__</tt> attribute.
If no dot is present, the entire <tt class="xref py py-attr docutils literal">tp_name</tt> field is made accessible as the
<tt class="xref py py-attr docutils literal">__name__</tt> attribute, and the <tt class="xref py py-attr docutils literal">__module__</tt> attribute is undefined
(unless explicitly set in the dictionary, as explained above). This means your
type will be impossible to pickle.
This field is not inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_basicsize">
Py_ssize_t <tt class="descname">PyTypeObject.tp_basicsize</tt><a class="headerlink" href="#PyTypeObject.tp_basicsize" title="Permalink to this definition">¶</a></dt>
<dt id="PyTypeObject.tp_itemsize">
Py_ssize_t <tt class="descname">PyTypeObject.tp_itemsize</tt><a class="headerlink" href="#PyTypeObject.tp_itemsize" title="Permalink to this definition">¶</a></dt>
<dd>These fields allow calculating the size in bytes of instances of the type.
There are two kinds of types: types with fixed-length instances have a zero
<tt class="xref py py-attr docutils literal">tp_itemsize</tt> field, types with variable-length instances have a non-zero
<tt class="xref py py-attr docutils literal">tp_itemsize</tt> field. For a type with fixed-length instances, all
instances have the same size, given in <tt class="xref py py-attr docutils literal">tp_basicsize</tt>.
For a type with variable-length instances, the instances must have an
<tt class="xref py py-attr docutils literal">ob_size</tt> field, and the instance size is <tt class="xref py py-attr docutils literal">tp_basicsize</tt> plus N
times <tt class="xref py py-attr docutils literal">tp_itemsize</tt>, where N is the &#8220;length&#8221; of the object. The value of
N is typically stored in the instance&#8217;s <tt class="xref py py-attr docutils literal">ob_size</tt> field. There are
exceptions: for example, long ints use a negative <tt class="xref py py-attr docutils literal">ob_size</tt> to indicate a
negative number, and N is <tt class="docutils literal">abs(ob_size)</tt> there. Also, the presence of an
<tt class="xref py py-attr docutils literal">ob_size</tt> field in the instance layout doesn&#8217;t mean that the instance
structure is variable-length (for example, the structure for the list type has
fixed-length instances, yet those instances have a meaningful <tt class="xref py py-attr docutils literal">ob_size</tt>
field).
The basic size includes the fields in the instance declared by the macro
<a class="reference internal" href="structures.html#PyObject_HEAD" title="PyObject_HEAD"><tt class="xref c c-macro docutils literal">PyObject_HEAD</tt></a> or <a class="reference internal" href="structures.html#PyObject_VAR_HEAD" title="PyObject_VAR_HEAD"><tt class="xref c c-macro docutils literal">PyObject_VAR_HEAD</tt></a> (whichever is used to
declare the instance struct) and this in turn includes the <tt class="xref py py-attr docutils literal">_ob_prev</tt> and
<tt class="xref py py-attr docutils literal">_ob_next</tt> fields if they are present. This means that the only correct
way to get an initializer for the <tt class="xref py py-attr docutils literal">tp_basicsize</tt> is to use the
<tt class="docutils literal">sizeof</tt> operator on the struct used to declare the instance layout.
The basic size does not include the GC header size (this is new in Python 2.2;
in 2.1 and 2.0, the GC header size was included in <tt class="xref py py-attr docutils literal">tp_basicsize</tt>).
These fields are inherited separately by subtypes. If the base type has a
non-zero <tt class="xref py py-attr docutils literal">tp_itemsize</tt>, it is generally not safe to set
<tt class="xref py py-attr docutils literal">tp_itemsize</tt> to a different non-zero value in a subtype (though this
depends on the implementation of the base type).
A note about alignment: if the variable items require a particular alignment,
this should be taken care of by the value of <tt class="xref py py-attr docutils literal">tp_basicsize</tt>. Example:
suppose a type implements an array of <tt class="docutils literal">double</tt>. <tt class="xref py py-attr docutils literal">tp_itemsize</tt> is
<tt class="docutils literal">sizeof(double)</tt>. It is the programmer&#8217;s responsibility that
<tt class="xref py py-attr docutils literal">tp_basicsize</tt> is a multiple of <tt class="docutils literal">sizeof(double)</tt> (assuming this is the
alignment requirement for <tt class="docutils literal">double</tt>).
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_dealloc">
destructor <tt class="descname">PyTypeObject.tp_dealloc</tt><a class="headerlink" href="#PyTypeObject.tp_dealloc" title="Permalink to this definition">¶</a></dt>
<dd>A pointer to the instance destructor function. This function must be defined
unless the type guarantees that its instances will never be deallocated (as is
the case for the singletons <tt class="docutils literal">None</tt> and <tt class="docutils literal">Ellipsis</tt>).
The destructor function is called by the <a class="reference internal" href="refcounting.html#Py_DECREF" title="Py_DECREF"><tt class="xref c c-func docutils literal">Py_DECREF()</tt></a> and
<a class="reference internal" href="refcounting.html#Py_XDECREF" title="Py_XDECREF"><tt class="xref c c-func docutils literal">Py_XDECREF()</tt></a> macros when the new reference count is zero. At this point,
the instance is still in existence, but there are no references to it. The
destructor function should free all references which the instance owns, free all
memory buffers owned by the instance (using the freeing function corresponding
to the allocation function used to allocate the buffer), and finally (as its
last action) call the type&#8217;s <tt class="xref py py-attr docutils literal">tp_free</tt> function. If the type is not
subtypable (doesn&#8217;t have the <a class="reference internal" href="#Py_TPFLAGS_BASETYPE" title="Py_TPFLAGS_BASETYPE"><tt class="xref py py-const docutils literal">Py_TPFLAGS_BASETYPE</tt></a> flag bit set), it is
permissible to call the object deallocator directly instead of via
<tt class="xref py py-attr docutils literal">tp_free</tt>. The object deallocator should be the one used to allocate the
instance; this is normally <a class="reference internal" href="allocation.html#PyObject_Del" title="PyObject_Del"><tt class="xref c c-func docutils literal">PyObject_Del()</tt></a> if the instance was allocated
using <a class="reference internal" href="allocation.html#PyObject_New" title="PyObject_New"><tt class="xref c c-func docutils literal">PyObject_New()</tt></a> or <tt class="xref c c-func docutils literal">PyObject_VarNew()</tt>, or
<a class="reference internal" href="gcsupport.html#PyObject_GC_Del" title="PyObject_GC_Del"><tt class="xref c c-func docutils literal">PyObject_GC_Del()</tt></a> if the instance was allocated using
<a class="reference internal" href="gcsupport.html#PyObject_GC_New" title="PyObject_GC_New"><tt class="xref c c-func docutils literal">PyObject_GC_New()</tt></a> or <a class="reference internal" href="gcsupport.html#PyObject_GC_NewVar" title="PyObject_GC_NewVar"><tt class="xref c c-func docutils literal">PyObject_GC_NewVar()</tt></a>.
This field is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_print">
printfunc <tt class="descname">PyTypeObject.tp_print</tt><a class="headerlink" href="#PyTypeObject.tp_print" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to the instance print function.
The print function is only called when the instance is printed to a real file;
when it is printed to a pseudo-file (like a <a class="reference internal" href="../library/stringio.html#module-StringIO" title="StringIO: Read and write strings as if they were files."><tt class="xref py py-class docutils literal">StringIO</tt></a> instance), the
instance&#8217;s <tt class="xref py py-attr docutils literal">tp_repr</tt> or <tt class="xref py py-attr docutils literal">tp_str</tt> function is called to convert it to
a string. These are also called when the type&#8217;s <tt class="xref py py-attr docutils literal">tp_print</tt> field is
NULL. A type should never implement <tt class="xref py py-attr docutils literal">tp_print</tt> in a way that produces
different output than <tt class="xref py py-attr docutils literal">tp_repr</tt> or <tt class="xref py py-attr docutils literal">tp_str</tt> would.
The print function is called with the same signature as <a class="reference internal" href="object.html#PyObject_Print" title="PyObject_Print"><tt class="xref c c-func docutils literal">PyObject_Print()</tt></a>:
<tt class="docutils literal">int tp_print(PyObject *self, FILE *file, int flags)</tt>. The self argument is
the instance to be printed. The file argument is the stdio file to which it
is to be printed. The flags argument is composed of flag bits. The only flag
bit currently defined is <tt class="xref py py-const docutils literal">Py_PRINT_RAW</tt>. When the <tt class="xref py py-const docutils literal">Py_PRINT_RAW</tt>
flag bit is set, the instance should be printed the same way as <tt class="xref py py-attr docutils literal">tp_str</tt>
would format it; when the <tt class="xref py py-const docutils literal">Py_PRINT_RAW</tt> flag bit is clear, the instance
should be printed the same was as <tt class="xref py py-attr docutils literal">tp_repr</tt> would format it. It should
return <tt class="docutils literal">-1</tt> and set an exception condition when an error occurred during the
comparison.
It is possible that the <tt class="xref py py-attr docutils literal">tp_print</tt> field will be deprecated. In any case,
it is recommended not to define <tt class="xref py py-attr docutils literal">tp_print</tt>, but instead to rely on
<tt class="xref py py-attr docutils literal">tp_repr</tt> and <tt class="xref py py-attr docutils literal">tp_str</tt> for printing.
This field is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_getattr">
getattrfunc <tt class="descname">PyTypeObject.tp_getattr</tt><a class="headerlink" href="#PyTypeObject.tp_getattr" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to the get-attribute-string function.
This field is deprecated. When it is defined, it should point to a function
that acts the same as the <tt class="xref py py-attr docutils literal">tp_getattro</tt> function, but taking a C string
instead of a Python string object to give the attribute name. The signature is
the same as for <a class="reference internal" href="object.html#PyObject_GetAttrString" title="PyObject_GetAttrString"><tt class="xref c c-func docutils literal">PyObject_GetAttrString()</tt></a>.
This field is inherited by subtypes together with <tt class="xref py py-attr docutils literal">tp_getattro</tt>: a subtype
inherits both <tt class="xref py py-attr docutils literal">tp_getattr</tt> and <tt class="xref py py-attr docutils literal">tp_getattro</tt> from its base type when
the subtype&#8217;s <tt class="xref py py-attr docutils literal">tp_getattr</tt> and <tt class="xref py py-attr docutils literal">tp_getattro</tt> are both NULL.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_setattr">
setattrfunc <tt class="descname">PyTypeObject.tp_setattr</tt><a class="headerlink" href="#PyTypeObject.tp_setattr" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to the set-attribute-string function.
This field is deprecated. When it is defined, it should point to a function
that acts the same as the <tt class="xref py py-attr docutils literal">tp_setattro</tt> function, but taking a C string
instead of a Python string object to give the attribute name. The signature is
the same as for <a class="reference internal" href="object.html#PyObject_SetAttrString" title="PyObject_SetAttrString"><tt class="xref c c-func docutils literal">PyObject_SetAttrString()</tt></a>.
This field is inherited by subtypes together with <tt class="xref py py-attr docutils literal">tp_setattro</tt>: a subtype
inherits both <tt class="xref py py-attr docutils literal">tp_setattr</tt> and <tt class="xref py py-attr docutils literal">tp_setattro</tt> from its base type when
the subtype&#8217;s <tt class="xref py py-attr docutils literal">tp_setattr</tt> and <tt class="xref py py-attr docutils literal">tp_setattro</tt> are both NULL.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_compare">
cmpfunc <tt class="descname">PyTypeObject.tp_compare</tt><a class="headerlink" href="#PyTypeObject.tp_compare" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to the three-way comparison function.
The signature is the same as for <a class="reference internal" href="object.html#PyObject_Compare" title="PyObject_Compare"><tt class="xref c c-func docutils literal">PyObject_Compare()</tt></a>. The function should
return <tt class="docutils literal">1</tt> if self greater than other, <tt class="docutils literal">0</tt> if self is equal to
other, and <tt class="docutils literal">-1</tt> if self less than other. It should return <tt class="docutils literal">-1</tt> and
set an exception condition when an error occurred during the comparison.
This field is inherited by subtypes together with <tt class="xref py py-attr docutils literal">tp_richcompare</tt> and
<tt class="xref py py-attr docutils literal">tp_hash</tt>: a subtypes inherits all three of <tt class="xref py py-attr docutils literal">tp_compare</tt>,
<tt class="xref py py-attr docutils literal">tp_richcompare</tt>, and <tt class="xref py py-attr docutils literal">tp_hash</tt> when the subtype&#8217;s
<tt class="xref py py-attr docutils literal">tp_compare</tt>, <tt class="xref py py-attr docutils literal">tp_richcompare</tt>, and <tt class="xref py py-attr docutils literal">tp_hash</tt> are all NULL.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_repr">
reprfunc <tt class="descname">PyTypeObject.tp_repr</tt><a class="headerlink" href="#PyTypeObject.tp_repr" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a function that implements the built-in function
<a class="reference internal" href="../library/repr.html#module-repr" title="repr: Alternate repr() implementation with size limits."><tt class="xref py py-func docutils literal">repr()</tt></a>.
The signature is the same as for <a class="reference internal" href="object.html#PyObject_Repr" title="PyObject_Repr"><tt class="xref c c-func docutils literal">PyObject_Repr()</tt></a>; it must return a string
or a Unicode object. Ideally, this function should return a string that, when
passed to <a class="reference internal" href="../library/functions.html#eval" title="eval"><tt class="xref py py-func docutils literal">eval()</tt></a>, given a suitable environment, returns an object with the
same value. If this is not feasible, it should return a string starting with
<tt class="docutils literal">'&lt;'</tt> and ending with <tt class="docutils literal">'&gt;'</tt> from which both the type and the value of the
object can be deduced.
When this field is not set, a string of the form <tt class="docutils literal">&lt;%s object at %p&gt;</tt> is
returned, where <tt class="docutils literal">%s</tt> is replaced by the type name, and <tt class="docutils literal">%p</tt> by the object&#8217;s
memory address.
This field is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="tp_as_number">
<a class="reference internal" href="#PyNumberMethods" title="PyNumberMethods">PyNumberMethods</a>* <tt class="descname">tp_as_number</tt><a class="headerlink" href="#tp_as_number" title="Permalink to this definition">¶</a></dt>
<dd>Pointer to an additional structure that contains fields relevant only to
objects which implement the number protocol. These fields are documented in
<a class="reference internal" href="#number-structs">Number Object Structures</a>.
The <tt class="xref py py-attr docutils literal">tp_as_number</tt> field is not inherited, but the contained fields are
inherited individually.
</dd></dl>

<dl class="member">
<dt id="tp_as_sequence">
<a class="reference internal" href="#PySequenceMethods" title="PySequenceMethods">PySequenceMethods</a>* <tt class="descname">tp_as_sequence</tt><a class="headerlink" href="#tp_as_sequence" title="Permalink to this definition">¶</a></dt>
<dd>Pointer to an additional structure that contains fields relevant only to
objects which implement the sequence protocol. These fields are documented
in <a class="reference internal" href="#sequence-structs">Sequence Object Structures</a>.
The <tt class="xref py py-attr docutils literal">tp_as_sequence</tt> field is not inherited, but the contained fields
are inherited individually.
</dd></dl>

<dl class="member">
<dt id="tp_as_mapping">
<a class="reference internal" href="#PyMappingMethods" title="PyMappingMethods">PyMappingMethods</a>* <tt class="descname">tp_as_mapping</tt><a class="headerlink" href="#tp_as_mapping" title="Permalink to this definition">¶</a></dt>
<dd>Pointer to an additional structure that contains fields relevant only to
objects which implement the mapping protocol. These fields are documented in
<a class="reference internal" href="#mapping-structs">Mapping Object Structures</a>.
The <tt class="xref py py-attr docutils literal">tp_as_mapping</tt> field is not inherited, but the contained fields
are inherited individually.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_hash">
hashfunc <tt class="descname">PyTypeObject.tp_hash</tt><a class="headerlink" href="#PyTypeObject.tp_hash" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a function that implements the built-in function
<a class="reference internal" href="../library/functions.html#hash" title="hash"><tt class="xref py py-func docutils literal">hash()</tt></a>.
The signature is the same as for <a class="reference internal" href="object.html#PyObject_Hash" title="PyObject_Hash"><tt class="xref c c-func docutils literal">PyObject_Hash()</tt></a>; it must return a C
long. The value <tt class="docutils literal">-1</tt> should not be returned as a normal return value; when an
error occurs during the computation of the hash value, the function should set
an exception and return <tt class="docutils literal">-1</tt>.
This field can be set explicitly to <a class="reference internal" href="object.html#PyObject_HashNotImplemented" title="PyObject_HashNotImplemented"><tt class="xref c c-func docutils literal">PyObject_HashNotImplemented()</tt></a> to
block inheritance of the hash method from a parent type. This is interpreted
as the equivalent of <tt class="docutils literal">__hash__ = None</tt> at the Python level, causing
<tt class="docutils literal">isinstance(o, collections.Hashable)</tt> to correctly return <tt class="docutils literal">False</tt>. Note
that the converse is also true - setting <tt class="docutils literal">__hash__ = None</tt> on a class at
the Python level will result in the <tt class="docutils literal">tp_hash</tt> slot being set to
<a class="reference internal" href="object.html#PyObject_HashNotImplemented" title="PyObject_HashNotImplemented"><tt class="xref c c-func docutils literal">PyObject_HashNotImplemented()</tt></a>.
When this field is not set, two possibilities exist: if the <tt class="xref py py-attr docutils literal">tp_compare</tt>
and <tt class="xref py py-attr docutils literal">tp_richcompare</tt> fields are both NULL, a default hash value based on
the object&#8217;s address is returned; otherwise, a <a class="reference internal" href="../library/exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><tt class="xref py py-exc docutils literal">TypeError</tt></a> is raised.
This field is inherited by subtypes together with <tt class="xref py py-attr docutils literal">tp_richcompare</tt> and
<tt class="xref py py-attr docutils literal">tp_compare</tt>: a subtypes inherits all three of <tt class="xref py py-attr docutils literal">tp_compare</tt>,
<tt class="xref py py-attr docutils literal">tp_richcompare</tt>, and <tt class="xref py py-attr docutils literal">tp_hash</tt>, when the subtype&#8217;s
<tt class="xref py py-attr docutils literal">tp_compare</tt>, <tt class="xref py py-attr docutils literal">tp_richcompare</tt> and <tt class="xref py py-attr docutils literal">tp_hash</tt> are all NULL.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_call">
ternaryfunc <tt class="descname">PyTypeObject.tp_call</tt><a class="headerlink" href="#PyTypeObject.tp_call" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a function that implements calling the object. This
should be NULL if the object is not callable. The signature is the same as
for <a class="reference internal" href="object.html#PyObject_Call" title="PyObject_Call"><tt class="xref c c-func docutils literal">PyObject_Call()</tt></a>.
This field is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_str">
reprfunc <tt class="descname">PyTypeObject.tp_str</tt><a class="headerlink" href="#PyTypeObject.tp_str" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a function that implements the built-in operation
<a class="reference internal" href="../library/functions.html#str" title="str"><tt class="xref py py-func docutils literal">str()</tt></a>. (Note that <a class="reference internal" href="../library/functions.html#str" title="str"><tt class="xref py py-class docutils literal">str</tt></a> is a type now, and <a class="reference internal" href="../library/functions.html#str" title="str"><tt class="xref py py-func docutils literal">str()</tt></a> calls the
constructor for that type. This constructor calls <a class="reference internal" href="object.html#PyObject_Str" title="PyObject_Str"><tt class="xref c c-func docutils literal">PyObject_Str()</tt></a> to do
the actual work, and <a class="reference internal" href="object.html#PyObject_Str" title="PyObject_Str"><tt class="xref c c-func docutils literal">PyObject_Str()</tt></a> will call this handler.)
The signature is the same as for <a class="reference internal" href="object.html#PyObject_Str" title="PyObject_Str"><tt class="xref c c-func docutils literal">PyObject_Str()</tt></a>; it must return a string
or a Unicode object. This function should return a &#8220;friendly&#8221; string
representation of the object, as this is the representation that will be used by
the print statement.
When this field is not set, <a class="reference internal" href="object.html#PyObject_Repr" title="PyObject_Repr"><tt class="xref c c-func docutils literal">PyObject_Repr()</tt></a> is called to return a string
representation.
This field is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_getattro">
getattrofunc <tt class="descname">PyTypeObject.tp_getattro</tt><a class="headerlink" href="#PyTypeObject.tp_getattro" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to the get-attribute function.
The signature is the same as for <a class="reference internal" href="object.html#PyObject_GetAttr" title="PyObject_GetAttr"><tt class="xref c c-func docutils literal">PyObject_GetAttr()</tt></a>. It is usually
convenient to set this field to <a class="reference internal" href="object.html#PyObject_GenericGetAttr" title="PyObject_GenericGetAttr"><tt class="xref c c-func docutils literal">PyObject_GenericGetAttr()</tt></a>, which
implements the normal way of looking for object attributes.
This field is inherited by subtypes together with <tt class="xref py py-attr docutils literal">tp_getattr</tt>: a subtype
inherits both <tt class="xref py py-attr docutils literal">tp_getattr</tt> and <tt class="xref py py-attr docutils literal">tp_getattro</tt> from its base type when
the subtype&#8217;s <tt class="xref py py-attr docutils literal">tp_getattr</tt> and <tt class="xref py py-attr docutils literal">tp_getattro</tt> are both NULL.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_setattro">
setattrofunc <tt class="descname">PyTypeObject.tp_setattro</tt><a class="headerlink" href="#PyTypeObject.tp_setattro" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to the set-attribute function.
The signature is the same as for <a class="reference internal" href="object.html#PyObject_SetAttr" title="PyObject_SetAttr"><tt class="xref c c-func docutils literal">PyObject_SetAttr()</tt></a>. It is usually
convenient to set this field to <a class="reference internal" href="object.html#PyObject_GenericSetAttr" title="PyObject_GenericSetAttr"><tt class="xref c c-func docutils literal">PyObject_GenericSetAttr()</tt></a>, which
implements the normal way of setting object attributes.
This field is inherited by subtypes together with <tt class="xref py py-attr docutils literal">tp_setattr</tt>: a subtype
inherits both <tt class="xref py py-attr docutils literal">tp_setattr</tt> and <tt class="xref py py-attr docutils literal">tp_setattro</tt> from its base type when
the subtype&#8217;s <tt class="xref py py-attr docutils literal">tp_setattr</tt> and <tt class="xref py py-attr docutils literal">tp_setattro</tt> are both NULL.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_as_buffer">
<a class="reference internal" href="#PyBufferProcs" title="PyBufferProcs">PyBufferProcs</a>* <tt class="descname">PyTypeObject.tp_as_buffer</tt><a class="headerlink" href="#PyTypeObject.tp_as_buffer" title="Permalink to this definition">¶</a></dt>
<dd>Pointer to an additional structure that contains fields relevant only to objects
which implement the buffer interface. These fields are documented in
<a class="reference internal" href="#buffer-structs">Buffer Object Structures</a>.
The <tt class="xref py py-attr docutils literal">tp_as_buffer</tt> field is not inherited, but the contained fields are
inherited individually.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_flags">
long <tt class="descname">PyTypeObject.tp_flags</tt><a class="headerlink" href="#PyTypeObject.tp_flags" title="Permalink to this definition">¶</a></dt>
<dd>This field is a bit mask of various flags. Some flags indicate variant
semantics for certain situations; others are used to indicate that certain
fields in the type object (or in the extension structures referenced via
<tt class="xref py py-attr docutils literal">tp_as_number</tt>, <tt class="xref py py-attr docutils literal">tp_as_sequence</tt>, <tt class="xref py py-attr docutils literal">tp_as_mapping</tt>, and
<tt class="xref py py-attr docutils literal">tp_as_buffer</tt>) that were historically not always present are valid; if
such a flag bit is clear, the type fields it guards must not be accessed and
must be considered to have a zero or NULL value instead.
Inheritance of this field is complicated. Most flag bits are inherited
individually, i.e. if the base type has a flag bit set, the subtype inherits
this flag bit. The flag bits that pertain to extension structures are strictly
inherited if the extension structure is inherited, i.e. the base type&#8217;s value of
the flag bit is copied into the subtype together with a pointer to the extension
structure. The <a class="reference internal" href="#Py_TPFLAGS_HAVE_GC" title="Py_TPFLAGS_HAVE_GC"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GC</tt></a> flag bit is inherited together with
the <tt class="xref py py-attr docutils literal">tp_traverse</tt> and <tt class="xref py py-attr docutils literal">tp_clear</tt> fields, i.e. if the
<a class="reference internal" href="#Py_TPFLAGS_HAVE_GC" title="Py_TPFLAGS_HAVE_GC"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GC</tt></a> flag bit is clear in the subtype and the
<tt class="xref py py-attr docutils literal">tp_traverse</tt> and <tt class="xref py py-attr docutils literal">tp_clear</tt> fields in the subtype exist (as
indicated by the <a class="reference internal" href="#Py_TPFLAGS_HAVE_RICHCOMPARE" title="Py_TPFLAGS_HAVE_RICHCOMPARE"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_RICHCOMPARE</tt></a> flag bit) and have NULL
values.
The following bit masks are currently defined; these can be ORed together using
the <tt class="docutils literal">|</tt> operator to form the value of the <tt class="xref py py-attr docutils literal">tp_flags</tt> field. The macro
<a class="reference internal" href="type.html#PyType_HasFeature" title="PyType_HasFeature"><tt class="xref c c-func docutils literal">PyType_HasFeature()</tt></a> takes a type and a flags value, tp and f, and
checks whether <tt class="docutils literal">tp-&gt;tp_flags &amp; f</tt> is non-zero.
<dl class="data">
<dt id="Py_TPFLAGS_HAVE_GETCHARBUFFER">
<tt class="descname">Py_TPFLAGS_HAVE_GETCHARBUFFER</tt><a class="headerlink" href="#Py_TPFLAGS_HAVE_GETCHARBUFFER" title="Permalink to this definition">¶</a></dt>
<dd>If this bit is set, the <a class="reference internal" href="#PyBufferProcs" title="PyBufferProcs"><tt class="xref c c-type docutils literal">PyBufferProcs</tt></a> struct referenced by
<tt class="xref py py-attr docutils literal">tp_as_buffer</tt> has the <tt class="xref py py-attr docutils literal">bf_getcharbuffer</tt> field.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_HAVE_SEQUENCE_IN">
<tt class="descname">Py_TPFLAGS_HAVE_SEQUENCE_IN</tt><a class="headerlink" href="#Py_TPFLAGS_HAVE_SEQUENCE_IN" title="Permalink to this definition">¶</a></dt>
<dd>If this bit is set, the <a class="reference internal" href="#PySequenceMethods" title="PySequenceMethods"><tt class="xref c c-type docutils literal">PySequenceMethods</tt></a> struct referenced by
<tt class="xref py py-attr docutils literal">tp_as_sequence</tt> has the <tt class="xref py py-attr docutils literal">sq_contains</tt> field.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_GC">
<tt class="descname">Py_TPFLAGS_GC</tt><a class="headerlink" href="#Py_TPFLAGS_GC" title="Permalink to this definition">¶</a></dt>
<dd>This bit is obsolete. The bit it used to name is no longer in use. The symbol
is now defined as zero.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_HAVE_INPLACEOPS">
<tt class="descname">Py_TPFLAGS_HAVE_INPLACEOPS</tt><a class="headerlink" href="#Py_TPFLAGS_HAVE_INPLACEOPS" title="Permalink to this definition">¶</a></dt>
<dd>If this bit is set, the <a class="reference internal" href="#PySequenceMethods" title="PySequenceMethods"><tt class="xref c c-type docutils literal">PySequenceMethods</tt></a> struct referenced by
<tt class="xref py py-attr docutils literal">tp_as_sequence</tt> and the <a class="reference internal" href="#PyNumberMethods" title="PyNumberMethods"><tt class="xref c c-type docutils literal">PyNumberMethods</tt></a> structure referenced by
<tt class="xref py py-attr docutils literal">tp_as_number</tt> contain the fields for in-place operators. In particular,
this means that the <a class="reference internal" href="#PyNumberMethods" title="PyNumberMethods"><tt class="xref c c-type docutils literal">PyNumberMethods</tt></a> structure has the fields
<tt class="xref py py-attr docutils literal">nb_inplace_add</tt>, <tt class="xref py py-attr docutils literal">nb_inplace_subtract</tt>,
<tt class="xref py py-attr docutils literal">nb_inplace_multiply</tt>, <tt class="xref py py-attr docutils literal">nb_inplace_divide</tt>,
<tt class="xref py py-attr docutils literal">nb_inplace_remainder</tt>, <tt class="xref py py-attr docutils literal">nb_inplace_power</tt>,
<tt class="xref py py-attr docutils literal">nb_inplace_lshift</tt>, <tt class="xref py py-attr docutils literal">nb_inplace_rshift</tt>, <tt class="xref py py-attr docutils literal">nb_inplace_and</tt>,
<tt class="xref py py-attr docutils literal">nb_inplace_xor</tt>, and <tt class="xref py py-attr docutils literal">nb_inplace_or</tt>; and the
<a class="reference internal" href="#PySequenceMethods" title="PySequenceMethods"><tt class="xref c c-type docutils literal">PySequenceMethods</tt></a> struct has the fields <tt class="xref py py-attr docutils literal">sq_inplace_concat</tt> and
<tt class="xref py py-attr docutils literal">sq_inplace_repeat</tt>.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_CHECKTYPES">
<tt class="descname">Py_TPFLAGS_CHECKTYPES</tt><a class="headerlink" href="#Py_TPFLAGS_CHECKTYPES" title="Permalink to this definition">¶</a></dt>
<dd>If this bit is set, the binary and ternary operations in the
<a class="reference internal" href="#PyNumberMethods" title="PyNumberMethods"><tt class="xref c c-type docutils literal">PyNumberMethods</tt></a> structure referenced by <tt class="xref py py-attr docutils literal">tp_as_number</tt> accept
arguments of arbitrary object types, and do their own type conversions if
needed. If this bit is clear, those operations require that all arguments have
the current type as their type, and the caller is supposed to perform a coercion
operation first. This applies to <tt class="xref py py-attr docutils literal">nb_add</tt>, <tt class="xref py py-attr docutils literal">nb_subtract</tt>,
<tt class="xref py py-attr docutils literal">nb_multiply</tt>, <tt class="xref py py-attr docutils literal">nb_divide</tt>, <tt class="xref py py-attr docutils literal">nb_remainder</tt>, <tt class="xref py py-attr docutils literal">nb_divmod</tt>,
<tt class="xref py py-attr docutils literal">nb_power</tt>, <tt class="xref py py-attr docutils literal">nb_lshift</tt>, <tt class="xref py py-attr docutils literal">nb_rshift</tt>, <tt class="xref py py-attr docutils literal">nb_and</tt>,
<tt class="xref py py-attr docutils literal">nb_xor</tt>, and <tt class="xref py py-attr docutils literal">nb_or</tt>.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_HAVE_RICHCOMPARE">
<tt class="descname">Py_TPFLAGS_HAVE_RICHCOMPARE</tt><a class="headerlink" href="#Py_TPFLAGS_HAVE_RICHCOMPARE" title="Permalink to this definition">¶</a></dt>
<dd>If this bit is set, the type object has the <tt class="xref py py-attr docutils literal">tp_richcompare</tt> field, as
well as the <tt class="xref py py-attr docutils literal">tp_traverse</tt> and the <tt class="xref py py-attr docutils literal">tp_clear</tt> fields.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_HAVE_WEAKREFS">
<tt class="descname">Py_TPFLAGS_HAVE_WEAKREFS</tt><a class="headerlink" href="#Py_TPFLAGS_HAVE_WEAKREFS" title="Permalink to this definition">¶</a></dt>
<dd>If this bit is set, the <tt class="xref py py-attr docutils literal">tp_weaklistoffset</tt> field is defined. Instances
of a type are weakly referenceable if the type&#8217;s <tt class="xref py py-attr docutils literal">tp_weaklistoffset</tt> field
has a value greater than zero.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_HAVE_ITER">
<tt class="descname">Py_TPFLAGS_HAVE_ITER</tt><a class="headerlink" href="#Py_TPFLAGS_HAVE_ITER" title="Permalink to this definition">¶</a></dt>
<dd>If this bit is set, the type object has the <tt class="xref py py-attr docutils literal">tp_iter</tt> and
<tt class="xref py py-attr docutils literal">tp_iternext</tt> fields.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_HAVE_CLASS">
<tt class="descname">Py_TPFLAGS_HAVE_CLASS</tt><a class="headerlink" href="#Py_TPFLAGS_HAVE_CLASS" title="Permalink to this definition">¶</a></dt>
<dd>If this bit is set, the type object has several new fields defined starting in
Python 2.2: <tt class="xref py py-attr docutils literal">tp_methods</tt>, <tt class="xref py py-attr docutils literal">tp_members</tt>, <tt class="xref py py-attr docutils literal">tp_getset</tt>,
<tt class="xref py py-attr docutils literal">tp_base</tt>, <tt class="xref py py-attr docutils literal">tp_dict</tt>, <tt class="xref py py-attr docutils literal">tp_descr_get</tt>, <tt class="xref py py-attr docutils literal">tp_descr_set</tt>,
<tt class="xref py py-attr docutils literal">tp_dictoffset</tt>, <tt class="xref py py-attr docutils literal">tp_init</tt>, <tt class="xref py py-attr docutils literal">tp_alloc</tt>, <tt class="xref py py-attr docutils literal">tp_new</tt>,
<tt class="xref py py-attr docutils literal">tp_free</tt>, <tt class="xref py py-attr docutils literal">tp_is_gc</tt>, <tt class="xref py py-attr docutils literal">tp_bases</tt>, <tt class="xref py py-attr docutils literal">tp_mro</tt>,
<tt class="xref py py-attr docutils literal">tp_cache</tt>, <tt class="xref py py-attr docutils literal">tp_subclasses</tt>, and <tt class="xref py py-attr docutils literal">tp_weaklist</tt>.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_HEAPTYPE">
<tt class="descname">Py_TPFLAGS_HEAPTYPE</tt><a class="headerlink" href="#Py_TPFLAGS_HEAPTYPE" title="Permalink to this definition">¶</a></dt>
<dd>This bit is set when the type object itself is allocated on the heap. In this
case, the <tt class="xref py py-attr docutils literal">ob_type</tt> field of its instances is considered a reference to
the type, and the type object is INCREF&#8217;ed when a new instance is created, and
DECREF&#8217;ed when an instance is destroyed (this does not apply to instances of
subtypes; only the type referenced by the instance&#8217;s ob_type gets INCREF&#8217;ed or
DECREF&#8217;ed).
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_BASETYPE">
<tt class="descname">Py_TPFLAGS_BASETYPE</tt><a class="headerlink" href="#Py_TPFLAGS_BASETYPE" title="Permalink to this definition">¶</a></dt>
<dd>This bit is set when the type can be used as the base type of another type. If
this bit is clear, the type cannot be subtyped (similar to a &#8220;final&#8221; class in
Java).
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_READY">
<tt class="descname">Py_TPFLAGS_READY</tt><a class="headerlink" href="#Py_TPFLAGS_READY" title="Permalink to this definition">¶</a></dt>
<dd>This bit is set when the type object has been fully initialized by
<a class="reference internal" href="type.html#PyType_Ready" title="PyType_Ready"><tt class="xref c c-func docutils literal">PyType_Ready()</tt></a>.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_READYING">
<tt class="descname">Py_TPFLAGS_READYING</tt><a class="headerlink" href="#Py_TPFLAGS_READYING" title="Permalink to this definition">¶</a></dt>
<dd>This bit is set while <a class="reference internal" href="type.html#PyType_Ready" title="PyType_Ready"><tt class="xref c c-func docutils literal">PyType_Ready()</tt></a> is in the process of initializing
the type object.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_HAVE_GC">
<tt class="descname">Py_TPFLAGS_HAVE_GC</tt><a class="headerlink" href="#Py_TPFLAGS_HAVE_GC" title="Permalink to this definition">¶</a></dt>
<dd>This bit is set when the object supports garbage collection. If this bit
is set, instances must be created using <a class="reference internal" href="gcsupport.html#PyObject_GC_New" title="PyObject_GC_New"><tt class="xref c c-func docutils literal">PyObject_GC_New()</tt></a> and
destroyed using <a class="reference internal" href="gcsupport.html#PyObject_GC_Del" title="PyObject_GC_Del"><tt class="xref c c-func docutils literal">PyObject_GC_Del()</tt></a>. More information in section
<a class="reference internal" href="gcsupport.html#supporting-cycle-detection">Supporting Cyclic Garbage Collection</a>. This bit also implies that the
GC-related fields <tt class="xref py py-attr docutils literal">tp_traverse</tt> and <tt class="xref py py-attr docutils literal">tp_clear</tt> are present in
the type object; but those fields also exist when
<a class="reference internal" href="#Py_TPFLAGS_HAVE_GC" title="Py_TPFLAGS_HAVE_GC"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GC</tt></a> is clear but
<a class="reference internal" href="#Py_TPFLAGS_HAVE_RICHCOMPARE" title="Py_TPFLAGS_HAVE_RICHCOMPARE"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_RICHCOMPARE</tt></a> is set.
</dd></dl>

<dl class="data">
<dt id="Py_TPFLAGS_DEFAULT">
<tt class="descname">Py_TPFLAGS_DEFAULT</tt><a class="headerlink" href="#Py_TPFLAGS_DEFAULT" title="Permalink to this definition">¶</a></dt>
<dd>This is a bitmask of all the bits that pertain to the existence of certain
fields in the type object and its extension structures. Currently, it includes
the following bits: <a class="reference internal" href="#Py_TPFLAGS_HAVE_GETCHARBUFFER" title="Py_TPFLAGS_HAVE_GETCHARBUFFER"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GETCHARBUFFER</tt></a>,
<a class="reference internal" href="#Py_TPFLAGS_HAVE_SEQUENCE_IN" title="Py_TPFLAGS_HAVE_SEQUENCE_IN"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_SEQUENCE_IN</tt></a>, <a class="reference internal" href="#Py_TPFLAGS_HAVE_INPLACEOPS" title="Py_TPFLAGS_HAVE_INPLACEOPS"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_INPLACEOPS</tt></a>,
<a class="reference internal" href="#Py_TPFLAGS_HAVE_RICHCOMPARE" title="Py_TPFLAGS_HAVE_RICHCOMPARE"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_RICHCOMPARE</tt></a>, <a class="reference internal" href="#Py_TPFLAGS_HAVE_WEAKREFS" title="Py_TPFLAGS_HAVE_WEAKREFS"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_WEAKREFS</tt></a>,
<a class="reference internal" href="#Py_TPFLAGS_HAVE_ITER" title="Py_TPFLAGS_HAVE_ITER"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_ITER</tt></a>, and <a class="reference internal" href="#Py_TPFLAGS_HAVE_CLASS" title="Py_TPFLAGS_HAVE_CLASS"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_CLASS</tt></a>.
</dd></dl>

</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_doc">
char* <tt class="descname">PyTypeObject.tp_doc</tt><a class="headerlink" href="#PyTypeObject.tp_doc" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a NUL-terminated C string giving the docstring for this
type object. This is exposed as the <tt class="xref py py-attr docutils literal">__doc__</tt> attribute on the type and
instances of the type.
This field is not inherited by subtypes.
</dd></dl>

The following three fields only exist if the
<a class="reference internal" href="#Py_TPFLAGS_HAVE_RICHCOMPARE" title="Py_TPFLAGS_HAVE_RICHCOMPARE"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_RICHCOMPARE</tt></a> flag bit is set.
<dl class="member">
<dt id="PyTypeObject.tp_traverse">
<a class="reference internal" href="gcsupport.html#traverseproc" title="traverseproc">traverseproc</a> <tt class="descname">PyTypeObject.tp_traverse</tt><a class="headerlink" href="#PyTypeObject.tp_traverse" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a traversal function for the garbage collector. This is
only used if the <a class="reference internal" href="#Py_TPFLAGS_HAVE_GC" title="Py_TPFLAGS_HAVE_GC"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GC</tt></a> flag bit is set. More information
about Python&#8217;s garbage collection scheme can be found in section
<a class="reference internal" href="gcsupport.html#supporting-cycle-detection">Supporting Cyclic Garbage Collection</a>.
The <tt class="xref py py-attr docutils literal">tp_traverse</tt> pointer is used by the garbage collector to detect
reference cycles. A typical implementation of a <tt class="xref py py-attr docutils literal">tp_traverse</tt> function
simply calls <a class="reference internal" href="gcsupport.html#Py_VISIT" title="Py_VISIT"><tt class="xref c c-func docutils literal">Py_VISIT()</tt></a> on each of the instance&#8217;s members that are Python
objects. For example, this is function <tt class="xref c c-func docutils literal">local_traverse()</tt> from the
<a class="reference internal" href="../library/thread.html#module-thread" title="thread: Create multiple threads of control within one interpreter."><tt class="xref py py-mod docutils literal">thread</tt></a> extension module:
<div class="highlight-c"><div class="highlight"><pre>static int
local_traverse(localobject *self, visitproc visit, void *arg)
{
 Py_VISIT(self-&gt;args);
 Py_VISIT(self-&gt;kw);
 Py_VISIT(self-&gt;dict);
 return 0;
}
</pre></div>
</div>
Note that <a class="reference internal" href="gcsupport.html#Py_VISIT" title="Py_VISIT"><tt class="xref c c-func docutils literal">Py_VISIT()</tt></a> is called only on those members that can participate
in reference cycles. Although there is also a <tt class="docutils literal">self-&gt;key</tt> member, it can only
be NULL or a Python string and therefore cannot be part of a reference cycle.
On the other hand, even if you know a member can never be part of a cycle, as a
debugging aid you may want to visit it anyway just so the <a class="reference internal" href="../library/gc.html#module-gc" title="gc: Interface to the cycle-detecting garbage collector."><tt class="xref py py-mod docutils literal">gc</tt></a> module&#8217;s
<tt class="xref py py-func docutils literal">get_referents()</tt> function will include it.
Note that <a class="reference internal" href="gcsupport.html#Py_VISIT" title="Py_VISIT"><tt class="xref c c-func docutils literal">Py_VISIT()</tt></a> requires the visit and arg parameters to
<tt class="xref c c-func docutils literal">local_traverse()</tt> to have these specific names; don&#8217;t name them just
anything.
This field is inherited by subtypes together with <tt class="xref py py-attr docutils literal">tp_clear</tt> and the
<a class="reference internal" href="#Py_TPFLAGS_HAVE_GC" title="Py_TPFLAGS_HAVE_GC"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GC</tt></a> flag bit: the flag bit, <tt class="xref py py-attr docutils literal">tp_traverse</tt>, and
<tt class="xref py py-attr docutils literal">tp_clear</tt> are all inherited from the base type if they are all zero in
the subtype and the subtype has the <a class="reference internal" href="#Py_TPFLAGS_HAVE_RICHCOMPARE" title="Py_TPFLAGS_HAVE_RICHCOMPARE"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_RICHCOMPARE</tt></a> flag
bit set.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_clear">
<a class="reference internal" href="gcsupport.html#inquiry" title="inquiry">inquiry</a> <tt class="descname">PyTypeObject.tp_clear</tt><a class="headerlink" href="#PyTypeObject.tp_clear" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a clear function for the garbage collector. This is only
used if the <a class="reference internal" href="#Py_TPFLAGS_HAVE_GC" title="Py_TPFLAGS_HAVE_GC"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GC</tt></a> flag bit is set.
The <tt class="xref py py-attr docutils literal">tp_clear</tt> member function is used to break reference cycles in cyclic
garbage detected by the garbage collector. Taken together, all <tt class="xref py py-attr docutils literal">tp_clear</tt>
functions in the system must combine to break all reference cycles. This is
subtle, and if in any doubt supply a <tt class="xref py py-attr docutils literal">tp_clear</tt> function. For example,
the tuple type does not implement a <tt class="xref py py-attr docutils literal">tp_clear</tt> function, because it&#8217;s
possible to prove that no reference cycle can be composed entirely of tuples.
Therefore the <tt class="xref py py-attr docutils literal">tp_clear</tt> functions of other types must be sufficient to
break any cycle containing a tuple. This isn&#8217;t immediately obvious, and there&#8217;s
rarely a good reason to avoid implementing <tt class="xref py py-attr docutils literal">tp_clear</tt>.
Implementations of <tt class="xref py py-attr docutils literal">tp_clear</tt> should drop the instance&#8217;s references to
those of its members that may be Python objects, and set its pointers to those
members to NULL, as in the following example:
<div class="highlight-c"><div class="highlight"><pre>static int
local_clear(localobject *self)
{
 Py_CLEAR(self-&gt;key);
 Py_CLEAR(self-&gt;args);
 Py_CLEAR(self-&gt;kw);
 Py_CLEAR(self-&gt;dict);
 return 0;
}
</pre></div>
</div>
The <a class="reference internal" href="refcounting.html#Py_CLEAR" title="Py_CLEAR"><tt class="xref c c-func docutils literal">Py_CLEAR()</tt></a> macro should be used, because clearing references is
delicate: the reference to the contained object must not be decremented until
after the pointer to the contained object is set to NULL. This is because
decrementing the reference count may cause the contained object to become trash,
triggering a chain of reclamation activity that may include invoking arbitrary
Python code (due to finalizers, or weakref callbacks, associated with the
contained object). If it&#8217;s possible for such code to reference self again,
it&#8217;s important that the pointer to the contained object be NULL at that time,
so that self knows the contained object can no longer be used. The
<a class="reference internal" href="refcounting.html#Py_CLEAR" title="Py_CLEAR"><tt class="xref c c-func docutils literal">Py_CLEAR()</tt></a> macro performs the operations in a safe order.
Because the goal of <tt class="xref py py-attr docutils literal">tp_clear</tt> functions is to break reference cycles,
it&#8217;s not necessary to clear contained objects like Python strings or Python
integers, which can&#8217;t participate in reference cycles. On the other hand, it may
be convenient to clear all contained Python objects, and write the type&#8217;s
<tt class="xref py py-attr docutils literal">tp_dealloc</tt> function to invoke <tt class="xref py py-attr docutils literal">tp_clear</tt>.
More information about Python&#8217;s garbage collection scheme can be found in
section <a class="reference internal" href="gcsupport.html#supporting-cycle-detection">Supporting Cyclic Garbage Collection</a>.
This field is inherited by subtypes together with <tt class="xref py py-attr docutils literal">tp_traverse</tt> and the
<a class="reference internal" href="#Py_TPFLAGS_HAVE_GC" title="Py_TPFLAGS_HAVE_GC"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GC</tt></a> flag bit: the flag bit, <tt class="xref py py-attr docutils literal">tp_traverse</tt>, and
<tt class="xref py py-attr docutils literal">tp_clear</tt> are all inherited from the base type if they are all zero in
the subtype and the subtype has the <a class="reference internal" href="#Py_TPFLAGS_HAVE_RICHCOMPARE" title="Py_TPFLAGS_HAVE_RICHCOMPARE"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_RICHCOMPARE</tt></a> flag
bit set.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_richcompare">
richcmpfunc <tt class="descname">PyTypeObject.tp_richcompare</tt><a class="headerlink" href="#PyTypeObject.tp_richcompare" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to the rich comparison function, whose signature is
<tt class="docutils literal">PyObject *tp_richcompare(PyObject *a, PyObject *b, int op)</tt>.
The function should return the result of the comparison (usually <tt class="docutils literal">Py_True</tt>
or <tt class="docutils literal">Py_False</tt>). If the comparison is undefined, it must return
<tt class="docutils literal">Py_NotImplemented</tt>, if another error occurred it must return <tt class="docutils literal">NULL</tt> and
set an exception condition.
<div class="admonition note">
Note
If you want to implement a type for which only a limited set of
comparisons makes sense (e.g. <tt class="docutils literal">==</tt> and <tt class="docutils literal">!=</tt>, but not <tt class="docutils literal">&lt;</tt> and
friends), directly raise <a class="reference internal" href="../library/exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><tt class="xref py py-exc docutils literal">TypeError</tt></a> in the rich comparison function.
</div>
This field is inherited by subtypes together with <tt class="xref py py-attr docutils literal">tp_compare</tt> and
<tt class="xref py py-attr docutils literal">tp_hash</tt>: a subtype inherits all three of <tt class="xref py py-attr docutils literal">tp_compare</tt>,
<tt class="xref py py-attr docutils literal">tp_richcompare</tt>, and <tt class="xref py py-attr docutils literal">tp_hash</tt>, when the subtype&#8217;s
<tt class="xref py py-attr docutils literal">tp_compare</tt>, <tt class="xref py py-attr docutils literal">tp_richcompare</tt>, and <tt class="xref py py-attr docutils literal">tp_hash</tt> are all NULL.
The following constants are defined to be used as the third argument for
<tt class="xref py py-attr docutils literal">tp_richcompare</tt> and for <a class="reference internal" href="object.html#PyObject_RichCompare" title="PyObject_RichCompare"><tt class="xref c c-func docutils literal">PyObject_RichCompare()</tt></a>:
<table border="1" class="docutils">
<colgroup>
<col width="57%" />
<col width="43%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Constant</th>
<th class="head">Comparison</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><tt class="xref py py-const docutils literal">Py_LT</tt></td>
<td><tt class="docutils literal">&lt;</tt></td>
</tr>
<tr class="row-odd"><td><tt class="xref py py-const docutils literal">Py_LE</tt></td>
<td><tt class="docutils literal">&lt;=</tt></td>
</tr>
<tr class="row-even"><td><tt class="xref py py-const docutils literal">Py_EQ</tt></td>
<td><tt class="docutils literal">==</tt></td>
</tr>
<tr class="row-odd"><td><tt class="xref py py-const docutils literal">Py_NE</tt></td>
<td><tt class="docutils literal">!=</tt></td>
</tr>
<tr class="row-even"><td><tt class="xref py py-const docutils literal">Py_GT</tt></td>
<td><tt class="docutils literal">&gt;</tt></td>
</tr>
<tr class="row-odd"><td><tt class="xref py py-const docutils literal">Py_GE</tt></td>
<td><tt class="docutils literal">&gt;=</tt></td>
</tr>
</tbody>
</table>
</dd></dl>

The next field only exists if the <a class="reference internal" href="#Py_TPFLAGS_HAVE_WEAKREFS" title="Py_TPFLAGS_HAVE_WEAKREFS"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_WEAKREFS</tt></a> flag bit is
set.
<dl class="member">
<dt id="PyTypeObject.tp_weaklistoffset">
long <tt class="descname">PyTypeObject.tp_weaklistoffset</tt><a class="headerlink" href="#PyTypeObject.tp_weaklistoffset" title="Permalink to this definition">¶</a></dt>
<dd>If the instances of this type are weakly referenceable, this field is greater
than zero and contains the offset in the instance structure of the weak
reference list head (ignoring the GC header, if present); this offset is used by
<tt class="xref c c-func docutils literal">PyObject_ClearWeakRefs()</tt> and the <tt class="xref c c-func docutils literal">PyWeakref_*()</tt> functions. The
instance structure needs to include a field of type <a class="reference internal" href="structures.html#PyObject" title="PyObject"><tt class="xref c c-type docutils literal">PyObject*</tt></a> which is
initialized to NULL.
Do not confuse this field with <tt class="xref py py-attr docutils literal">tp_weaklist</tt>; that is the list head for
weak references to the type object itself.
This field is inherited by subtypes, but see the rules listed below. A subtype
may override this offset; this means that the subtype uses a different weak
reference list head than the base type. Since the list head is always found via
<tt class="xref py py-attr docutils literal">tp_weaklistoffset</tt>, this should not be a problem.
When a type defined by a class statement has no <a class="reference internal" href="../reference/datamodel.html#__slots__" title="__slots__"><tt class="xref py py-attr docutils literal">__slots__</tt></a> declaration,
and none of its base types are weakly referenceable, the type is made weakly
referenceable by adding a weak reference list head slot to the instance layout
and setting the <tt class="xref py py-attr docutils literal">tp_weaklistoffset</tt> of that slot&#8217;s offset.
When a type&#8217;s <a class="reference internal" href="../reference/datamodel.html#__slots__" title="__slots__"><tt class="xref py py-attr docutils literal">__slots__</tt></a> declaration contains a slot named
<tt class="xref py py-attr docutils literal">__weakref__</tt>, that slot becomes the weak reference list head for
instances of the type, and the slot&#8217;s offset is stored in the type&#8217;s
<tt class="xref py py-attr docutils literal">tp_weaklistoffset</tt>.
When a type&#8217;s <a class="reference internal" href="../reference/datamodel.html#__slots__" title="__slots__"><tt class="xref py py-attr docutils literal">__slots__</tt></a> declaration does not contain a slot named
<tt class="xref py py-attr docutils literal">__weakref__</tt>, the type inherits its <tt class="xref py py-attr docutils literal">tp_weaklistoffset</tt> from its
base type.
</dd></dl>

The next two fields only exist if the <a class="reference internal" href="#Py_TPFLAGS_HAVE_ITER" title="Py_TPFLAGS_HAVE_ITER"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_ITER</tt></a> flag bit is
set.
<dl class="member">
<dt id="PyTypeObject.tp_iter">
getiterfunc <tt class="descname">PyTypeObject.tp_iter</tt><a class="headerlink" href="#PyTypeObject.tp_iter" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a function that returns an iterator for the object. Its
presence normally signals that the instances of this type are iterable (although
sequences may be iterable without this function, and classic instances always
have this function, even if they don&#8217;t define an <a class="reference internal" href="../reference/datamodel.html#object.__iter__" title="object.__iter__"><tt class="xref py py-meth docutils literal">__iter__()</tt></a> method).
This function has the same signature as <a class="reference internal" href="object.html#PyObject_GetIter" title="PyObject_GetIter"><tt class="xref c c-func docutils literal">PyObject_GetIter()</tt></a>.
This field is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_iternext">
iternextfunc <tt class="descname">PyTypeObject.tp_iternext</tt><a class="headerlink" href="#PyTypeObject.tp_iternext" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a function that returns the next item in an iterator.
When the iterator is exhausted, it must return NULL; a <a class="reference internal" href="../library/exceptions.html#exceptions.StopIteration" title="exceptions.StopIteration"><tt class="xref py py-exc docutils literal">StopIteration</tt></a>
exception may or may not be set. When another error occurs, it must return
NULL too. Its presence normally signals that the instances of this type
are iterators (although classic instances always have this function, even if
they don&#8217;t define a <a class="reference internal" href="../library/functions.html#next" title="next"><tt class="xref py py-meth docutils literal">next()</tt></a> method).
Iterator types should also define the <tt class="xref py py-attr docutils literal">tp_iter</tt> function, and that
function should return the iterator instance itself (not a new iterator
instance).
This function has the same signature as <a class="reference internal" href="iter.html#PyIter_Next" title="PyIter_Next"><tt class="xref c c-func docutils literal">PyIter_Next()</tt></a>.
This field is inherited by subtypes.
</dd></dl>

The next fields, up to and including <tt class="xref py py-attr docutils literal">tp_weaklist</tt>, only exist if the
<a class="reference internal" href="#Py_TPFLAGS_HAVE_CLASS" title="Py_TPFLAGS_HAVE_CLASS"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_CLASS</tt></a> flag bit is set.
<dl class="member">
<dt id="PyTypeObject.tp_methods">
struct <a class="reference internal" href="structures.html#PyMethodDef" title="PyMethodDef">PyMethodDef</a>* <tt class="descname">PyTypeObject.tp_methods</tt><a class="headerlink" href="#PyTypeObject.tp_methods" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a static NULL-terminated array of <a class="reference internal" href="structures.html#PyMethodDef" title="PyMethodDef"><tt class="xref c c-type docutils literal">PyMethodDef</tt></a>
structures, declaring regular methods of this type.
For each entry in the array, an entry is added to the type&#8217;s dictionary (see
<tt class="xref py py-attr docutils literal">tp_dict</tt> below) containing a method descriptor.
This field is not inherited by subtypes (methods are inherited through a
different mechanism).
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_members">
struct <a class="reference internal" href="structures.html#PyMemberDef" title="PyMemberDef">PyMemberDef</a>* <tt class="descname">PyTypeObject.tp_members</tt><a class="headerlink" href="#PyTypeObject.tp_members" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a static NULL-terminated array of <a class="reference internal" href="structures.html#PyMemberDef" title="PyMemberDef"><tt class="xref c c-type docutils literal">PyMemberDef</tt></a>
structures, declaring regular data members (fields or slots) of instances of
this type.
For each entry in the array, an entry is added to the type&#8217;s dictionary (see
<tt class="xref py py-attr docutils literal">tp_dict</tt> below) containing a member descriptor.
This field is not inherited by subtypes (members are inherited through a
different mechanism).
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_getset">
struct PyGetSetDef* <tt class="descname">PyTypeObject.tp_getset</tt><a class="headerlink" href="#PyTypeObject.tp_getset" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a static NULL-terminated array of <tt class="xref c c-type docutils literal">PyGetSetDef</tt>
structures, declaring computed attributes of instances of this type.
For each entry in the array, an entry is added to the type&#8217;s dictionary (see
<tt class="xref py py-attr docutils literal">tp_dict</tt> below) containing a getset descriptor.
This field is not inherited by subtypes (computed attributes are inherited
through a different mechanism).
Docs for PyGetSetDef:
<div class="highlight-c"><div class="highlight"><pre>typedef PyObject *(*getter)(PyObject *, void *);
typedef int (*setter)(PyObject *, PyObject *, void *);

typedef struct PyGetSetDef {
 char *name; /* attribute name */
 getter get; /* C function to get the attribute */
 setter set; /* C function to set the attribute */
 char *doc; /* optional doc string */
 void *closure; /* optional additional data for getter and setter */
} PyGetSetDef;
</pre></div>
</div>
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_base">
<a class="reference internal" href="type.html#PyTypeObject" title="PyTypeObject">PyTypeObject</a>* <tt class="descname">PyTypeObject.tp_base</tt><a class="headerlink" href="#PyTypeObject.tp_base" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a base type from which type properties are inherited. At
this level, only single inheritance is supported; multiple inheritance require
dynamically creating a type object by calling the metatype.
This field is not inherited by subtypes (obviously), but it defaults to
<tt class="docutils literal">&amp;PyBaseObject_Type</tt> (which to Python programmers is known as the type
<a class="reference internal" href="../library/functions.html#object" title="object"><tt class="xref py py-class docutils literal">object</tt></a>).
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_dict">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyTypeObject.tp_dict</tt><a class="headerlink" href="#PyTypeObject.tp_dict" title="Permalink to this definition">¶</a></dt>
<dd>The type&#8217;s dictionary is stored here by <a class="reference internal" href="type.html#PyType_Ready" title="PyType_Ready"><tt class="xref c c-func docutils literal">PyType_Ready()</tt></a>.
This field should normally be initialized to NULL before PyType_Ready is
called; it may also be initialized to a dictionary containing initial attributes
for the type. Once <a class="reference internal" href="type.html#PyType_Ready" title="PyType_Ready"><tt class="xref c c-func docutils literal">PyType_Ready()</tt></a> has initialized the type, extra
attributes for the type may be added to this dictionary only if they don&#8217;t
correspond to overloaded operations (like <a class="reference internal" href="../reference/datamodel.html#object.__add__" title="object.__add__"><tt class="xref py py-meth docutils literal">__add__()</tt></a>).
This field is not inherited by subtypes (though the attributes defined in here
are inherited through a different mechanism).
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_descr_get">
descrgetfunc <tt class="descname">PyTypeObject.tp_descr_get</tt><a class="headerlink" href="#PyTypeObject.tp_descr_get" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a &#8220;descriptor get&#8221; function.
The function signature is
<div class="highlight-c"><div class="highlight"><pre>PyObject * tp_descr_get(PyObject *self, PyObject *obj, PyObject *type);
</pre></div>
</div>
This field is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_descr_set">
descrsetfunc <tt class="descname">PyTypeObject.tp_descr_set</tt><a class="headerlink" href="#PyTypeObject.tp_descr_set" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a &#8220;descriptor set&#8221; function.
The function signature is
<div class="highlight-c"><div class="highlight"><pre>int tp_descr_set(PyObject *self, PyObject *obj, PyObject *value);
</pre></div>
</div>
This field is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_dictoffset">
long <tt class="descname">PyTypeObject.tp_dictoffset</tt><a class="headerlink" href="#PyTypeObject.tp_dictoffset" title="Permalink to this definition">¶</a></dt>
<dd>If the instances of this type have a dictionary containing instance variables,
this field is non-zero and contains the offset in the instances of the type of
the instance variable dictionary; this offset is used by
<a class="reference internal" href="object.html#PyObject_GenericGetAttr" title="PyObject_GenericGetAttr"><tt class="xref c c-func docutils literal">PyObject_GenericGetAttr()</tt></a>.
Do not confuse this field with <tt class="xref py py-attr docutils literal">tp_dict</tt>; that is the dictionary for
attributes of the type object itself.
If the value of this field is greater than zero, it specifies the offset from
the start of the instance structure. If the value is less than zero, it
specifies the offset from the end of the instance structure. A negative
offset is more expensive to use, and should only be used when the instance
structure contains a variable-length part. This is used for example to add an
instance variable dictionary to subtypes of <a class="reference internal" href="../library/functions.html#str" title="str"><tt class="xref py py-class docutils literal">str</tt></a> or <a class="reference internal" href="../library/functions.html#tuple" title="tuple"><tt class="xref py py-class docutils literal">tuple</tt></a>. Note
that the <tt class="xref py py-attr docutils literal">tp_basicsize</tt> field should account for the dictionary added to
the end in that case, even though the dictionary is not included in the basic
object layout. On a system with a pointer size of 4 bytes,
<tt class="xref py py-attr docutils literal">tp_dictoffset</tt> should be set to <tt class="docutils literal">-4</tt> to indicate that the dictionary is
at the very end of the structure.
The real dictionary offset in an instance can be computed from a negative
<tt class="xref py py-attr docutils literal">tp_dictoffset</tt> as follows:
<div class="highlight-c"><div class="highlight"><pre>dictoffset = tp_basicsize + abs(ob_size)*tp_itemsize + tp_dictoffset
if dictoffset is not aligned on sizeof(void*):
 round up to sizeof(void*)
</pre></div>
</div>
where <tt class="xref py py-attr docutils literal">tp_basicsize</tt>, <tt class="xref py py-attr docutils literal">tp_itemsize</tt> and <tt class="xref py py-attr docutils literal">tp_dictoffset</tt> are
taken from the type object, and <tt class="xref py py-attr docutils literal">ob_size</tt> is taken from the instance. The
absolute value is taken because long ints use the sign of <tt class="xref py py-attr docutils literal">ob_size</tt> to
store the sign of the number. (There&#8217;s never a need to do this calculation
yourself; it is done for you by <tt class="xref c c-func docutils literal">_PyObject_GetDictPtr()</tt>.)
This field is inherited by subtypes, but see the rules listed below. A subtype
may override this offset; this means that the subtype instances store the
dictionary at a difference offset than the base type. Since the dictionary is
always found via <tt class="xref py py-attr docutils literal">tp_dictoffset</tt>, this should not be a problem.
When a type defined by a class statement has no <a class="reference internal" href="../reference/datamodel.html#__slots__" title="__slots__"><tt class="xref py py-attr docutils literal">__slots__</tt></a> declaration,
and none of its base types has an instance variable dictionary, a dictionary
slot is added to the instance layout and the <tt class="xref py py-attr docutils literal">tp_dictoffset</tt> is set to
that slot&#8217;s offset.
When a type defined by a class statement has a <a class="reference internal" href="../reference/datamodel.html#__slots__" title="__slots__"><tt class="xref py py-attr docutils literal">__slots__</tt></a> declaration,
the type inherits its <tt class="xref py py-attr docutils literal">tp_dictoffset</tt> from its base type.
(Adding a slot named <tt class="xref py py-attr docutils literal">__dict__</tt> to the <a class="reference internal" href="../reference/datamodel.html#__slots__" title="__slots__"><tt class="xref py py-attr docutils literal">__slots__</tt></a> declaration does
not have the expected effect, it just causes confusion. Maybe this should be
added as a feature just like <tt class="xref py py-attr docutils literal">__weakref__</tt> though.)
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_init">
initproc <tt class="descname">PyTypeObject.tp_init</tt><a class="headerlink" href="#PyTypeObject.tp_init" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to an instance initialization function.
This function corresponds to the <a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><tt class="xref py py-meth docutils literal">__init__()</tt></a> method of classes. Like
<a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><tt class="xref py py-meth docutils literal">__init__()</tt></a>, it is possible to create an instance without calling
<a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><tt class="xref py py-meth docutils literal">__init__()</tt></a>, and it is possible to reinitialize an instance by calling its
<a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><tt class="xref py py-meth docutils literal">__init__()</tt></a> method again.
The function signature is
<div class="highlight-c"><div class="highlight"><pre>int tp_init(PyObject *self, PyObject *args, PyObject *kwds)
</pre></div>
</div>
The self argument is the instance to be initialized; the args and kwds
arguments represent positional and keyword arguments of the call to
<a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><tt class="xref py py-meth docutils literal">__init__()</tt></a>.
The <tt class="xref py py-attr docutils literal">tp_init</tt> function, if not NULL, is called when an instance is
created normally by calling its type, after the type&#8217;s <tt class="xref py py-attr docutils literal">tp_new</tt> function
has returned an instance of the type. If the <tt class="xref py py-attr docutils literal">tp_new</tt> function returns an
instance of some other type that is not a subtype of the original type, no
<tt class="xref py py-attr docutils literal">tp_init</tt> function is called; if <tt class="xref py py-attr docutils literal">tp_new</tt> returns an instance of a
subtype of the original type, the subtype&#8217;s <tt class="xref py py-attr docutils literal">tp_init</tt> is called. (VERSION
NOTE: described here is what is implemented in Python 2.2.1 and later. In
Python 2.2, the <tt class="xref py py-attr docutils literal">tp_init</tt> of the type of the object returned by
<tt class="xref py py-attr docutils literal">tp_new</tt> was always called, if not NULL.)
This field is inherited by subtypes.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_alloc">
allocfunc <tt class="descname">PyTypeObject.tp_alloc</tt><a class="headerlink" href="#PyTypeObject.tp_alloc" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to an instance allocation function.
The function signature is
<div class="highlight-c"><div class="highlight"><pre>PyObject *tp_alloc(PyTypeObject *self, Py_ssize_t nitems)
</pre></div>
</div>
The purpose of this function is to separate memory allocation from memory
initialization. It should return a pointer to a block of memory of adequate
length for the instance, suitably aligned, and initialized to zeros, but with
<tt class="xref py py-attr docutils literal">ob_refcnt</tt> set to <tt class="docutils literal">1</tt> and <tt class="xref py py-attr docutils literal">ob_type</tt> set to the type argument. If
the type&#8217;s <tt class="xref py py-attr docutils literal">tp_itemsize</tt> is non-zero, the object&#8217;s <tt class="xref py py-attr docutils literal">ob_size</tt> field
should be initialized to nitems and the length of the allocated memory block
should be <tt class="docutils literal">tp_basicsize + nitems*tp_itemsize</tt>, rounded up to a multiple of
<tt class="docutils literal">sizeof(void*)</tt>; otherwise, nitems is not used and the length of the block
should be <tt class="xref py py-attr docutils literal">tp_basicsize</tt>.
Do not use this function to do any other instance initialization, not even to
allocate additional memory; that should be done by <tt class="xref py py-attr docutils literal">tp_new</tt>.
This field is inherited by static subtypes, but not by dynamic subtypes
(subtypes created by a class statement); in the latter, this field is always set
to <a class="reference internal" href="type.html#PyType_GenericAlloc" title="PyType_GenericAlloc"><tt class="xref c c-func docutils literal">PyType_GenericAlloc()</tt></a>, to force a standard heap allocation strategy.
That is also the recommended value for statically defined types.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_new">
newfunc <tt class="descname">PyTypeObject.tp_new</tt><a class="headerlink" href="#PyTypeObject.tp_new" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to an instance creation function.
If this function is NULL for a particular type, that type cannot be called to
create new instances; presumably there is some other way to create instances,
like a factory function.
The function signature is
<div class="highlight-c"><div class="highlight"><pre>PyObject *tp_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds)
</pre></div>
</div>
The subtype argument is the type of the object being created; the args and
kwds arguments represent positional and keyword arguments of the call to the
type. Note that subtype doesn&#8217;t have to equal the type whose <tt class="xref py py-attr docutils literal">tp_new</tt>
function is called; it may be a subtype of that type (but not an unrelated
type).
The <tt class="xref py py-attr docutils literal">tp_new</tt> function should call <tt class="docutils literal">subtype-&gt;tp_alloc(subtype, nitems)</tt>
to allocate space for the object, and then do only as much further
initialization as is absolutely necessary. Initialization that can safely be
ignored or repeated should be placed in the <tt class="xref py py-attr docutils literal">tp_init</tt> handler. A good
rule of thumb is that for immutable types, all initialization should take place
in <tt class="xref py py-attr docutils literal">tp_new</tt>, while for mutable types, most initialization should be
deferred to <tt class="xref py py-attr docutils literal">tp_init</tt>.
This field is inherited by subtypes, except it is not inherited by static types
whose <tt class="xref py py-attr docutils literal">tp_base</tt> is NULL or <tt class="docutils literal">&amp;PyBaseObject_Type</tt>. The latter exception
is a precaution so that old extension types don&#8217;t become callable simply by
being linked with Python 2.2.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_free">
destructor <tt class="descname">PyTypeObject.tp_free</tt><a class="headerlink" href="#PyTypeObject.tp_free" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to an instance deallocation function.
The signature of this function has changed slightly: in Python 2.2 and 2.2.1,
its signature is <tt class="xref c c-type docutils literal">destructor</tt>:
<div class="highlight-c"><div class="highlight"><pre>void tp_free(PyObject *)
</pre></div>
</div>
In Python 2.3 and beyond, its signature is <tt class="xref c c-type docutils literal">freefunc</tt>:
<div class="highlight-c"><div class="highlight"><pre>void tp_free(void *)
</pre></div>
</div>
The only initializer that is compatible with both versions is <tt class="docutils literal">_PyObject_Del</tt>,
whose definition has suitably adapted in Python 2.3.
This field is inherited by static subtypes, but not by dynamic subtypes
(subtypes created by a class statement); in the latter, this field is set to a
deallocator suitable to match <a class="reference internal" href="type.html#PyType_GenericAlloc" title="PyType_GenericAlloc"><tt class="xref c c-func docutils literal">PyType_GenericAlloc()</tt></a> and the value of the
<a class="reference internal" href="#Py_TPFLAGS_HAVE_GC" title="Py_TPFLAGS_HAVE_GC"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GC</tt></a> flag bit.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_is_gc">
<a class="reference internal" href="gcsupport.html#inquiry" title="inquiry">inquiry</a> <tt class="descname">PyTypeObject.tp_is_gc</tt><a class="headerlink" href="#PyTypeObject.tp_is_gc" title="Permalink to this definition">¶</a></dt>
<dd>An optional pointer to a function called by the garbage collector.
The garbage collector needs to know whether a particular object is collectible
or not. Normally, it is sufficient to look at the object&#8217;s type&#8217;s
<tt class="xref py py-attr docutils literal">tp_flags</tt> field, and check the <a class="reference internal" href="#Py_TPFLAGS_HAVE_GC" title="Py_TPFLAGS_HAVE_GC"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GC</tt></a> flag bit. But
some types have a mixture of statically and dynamically allocated instances, and
the statically allocated instances are not collectible. Such types should
define this function; it should return <tt class="docutils literal">1</tt> for a collectible instance, and
<tt class="docutils literal">0</tt> for a non-collectible instance. The signature is
<div class="highlight-c"><div class="highlight"><pre>int tp_is_gc(PyObject *self)
</pre></div>
</div>
(The only example of this are types themselves. The metatype,
<a class="reference internal" href="type.html#PyType_Type" title="PyType_Type"><tt class="xref c c-data docutils literal">PyType_Type</tt></a>, defines this function to distinguish between statically
and dynamically allocated types.)
This field is inherited by subtypes. (VERSION NOTE: in Python 2.2, it was not
inherited. It is inherited in 2.2.1 and later versions.)
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_bases">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyTypeObject.tp_bases</tt><a class="headerlink" href="#PyTypeObject.tp_bases" title="Permalink to this definition">¶</a></dt>
<dd>Tuple of base types.
This is set for types created by a class statement. It should be NULL for
statically defined types.
This field is not inherited.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_mro">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyTypeObject.tp_mro</tt><a class="headerlink" href="#PyTypeObject.tp_mro" title="Permalink to this definition">¶</a></dt>
<dd>Tuple containing the expanded set of base types, starting with the type itself
and ending with <a class="reference internal" href="../library/functions.html#object" title="object"><tt class="xref py py-class docutils literal">object</tt></a>, in Method Resolution Order.
This field is not inherited; it is calculated fresh by <a class="reference internal" href="type.html#PyType_Ready" title="PyType_Ready"><tt class="xref c c-func docutils literal">PyType_Ready()</tt></a>.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_cache">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyTypeObject.tp_cache</tt><a class="headerlink" href="#PyTypeObject.tp_cache" title="Permalink to this definition">¶</a></dt>
<dd>Unused. Not inherited. Internal use only.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_subclasses">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyTypeObject.tp_subclasses</tt><a class="headerlink" href="#PyTypeObject.tp_subclasses" title="Permalink to this definition">¶</a></dt>
<dd>List of weak references to subclasses. Not inherited. Internal use only.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_weaklist">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyTypeObject.tp_weaklist</tt><a class="headerlink" href="#PyTypeObject.tp_weaklist" title="Permalink to this definition">¶</a></dt>
<dd>Weak reference list head, for weak references to this type object. Not
inherited. Internal use only.
</dd></dl>

The remaining fields are only defined if the feature test macro
<tt class="xref py py-const docutils literal">COUNT_ALLOCS</tt> is defined, and are for internal use only. They are
documented here for completeness. None of these fields are inherited by
subtypes.
<dl class="member">
<dt id="PyTypeObject.tp_allocs">
Py_ssize_t <tt class="descname">PyTypeObject.tp_allocs</tt><a class="headerlink" href="#PyTypeObject.tp_allocs" title="Permalink to this definition">¶</a></dt>
<dd>Number of allocations.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_frees">
Py_ssize_t <tt class="descname">PyTypeObject.tp_frees</tt><a class="headerlink" href="#PyTypeObject.tp_frees" title="Permalink to this definition">¶</a></dt>
<dd>Number of frees.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_maxalloc">
Py_ssize_t <tt class="descname">PyTypeObject.tp_maxalloc</tt><a class="headerlink" href="#PyTypeObject.tp_maxalloc" title="Permalink to this definition">¶</a></dt>
<dd>Maximum simultaneously allocated objects.
</dd></dl>

<dl class="member">
<dt id="PyTypeObject.tp_next">
<a class="reference internal" href="type.html#PyTypeObject" title="PyTypeObject">PyTypeObject</a>* <tt class="descname">PyTypeObject.tp_next</tt><a class="headerlink" href="#PyTypeObject.tp_next" title="Permalink to this definition">¶</a></dt>
<dd>Pointer to the next type object with a non-zero <tt class="xref py py-attr docutils literal">tp_allocs</tt> field.
</dd></dl>

Also, note that, in a garbage collected Python, tp_dealloc may be called from
any Python thread, not just the thread which created the object (if the object
becomes part of a refcount cycle, that cycle might be collected by a garbage
collection on any thread). This is not a problem for Python API calls, since
the thread on which tp_dealloc is called will own the Global Interpreter Lock
(GIL). However, if the object being destroyed in turn destroys objects from some
other C or C++ library, care should be taken to ensure that destroying those
objects on the thread which called tp_dealloc will not violate any assumptions
of the library.
</div>
<div class="section" id="number-object-structures">
<h1>Number Object Structures<a class="headerlink" href="#number-object-structures" title="Permalink to this headline">¶</a></h1>
<dl class="type">
<dt id="PyNumberMethods">
<tt class="descname">PyNumberMethods</tt><a class="headerlink" href="#PyNumberMethods" title="Permalink to this definition">¶</a></dt>
<dd>This structure holds pointers to the functions which an object uses to
implement the number protocol. Almost every function below is used by the
function of similar name documented in the <a class="reference internal" href="number.html#number">Number Protocol</a> section.
Here is the structure definition:
<div class="highlight-c"><div class="highlight"><pre>typedef struct {
 binaryfunc nb_add;
 binaryfunc nb_subtract;
 binaryfunc nb_multiply;
 binaryfunc nb_divide;
 binaryfunc nb_remainder;
 binaryfunc nb_divmod;
 ternaryfunc nb_power;
 unaryfunc nb_negative;
 unaryfunc nb_positive;
 unaryfunc nb_absolute;
 inquiry nb_nonzero; /* Used by PyObject_IsTrue */
 unaryfunc nb_invert;
 binaryfunc nb_lshift;
 binaryfunc nb_rshift;
 binaryfunc nb_and;
 binaryfunc nb_xor;
 binaryfunc nb_or;
 coercion nb_coerce; /* Used by the coerce() function */
 unaryfunc nb_int;
 unaryfunc nb_long;
 unaryfunc nb_float;
 unaryfunc nb_oct;
 unaryfunc nb_hex;

/* Added in release 2.0 */
 binaryfunc nb_inplace_add;
 binaryfunc nb_inplace_subtract;
 binaryfunc nb_inplace_multiply;
 binaryfunc nb_inplace_divide;
 binaryfunc nb_inplace_remainder;
 ternaryfunc nb_inplace_power;
 binaryfunc nb_inplace_lshift;
 binaryfunc nb_inplace_rshift;
 binaryfunc nb_inplace_and;
 binaryfunc nb_inplace_xor;
 binaryfunc nb_inplace_or;

/* Added in release 2.2 */
 binaryfunc nb_floor_divide;
 binaryfunc nb_true_divide;
 binaryfunc nb_inplace_floor_divide;
 binaryfunc nb_inplace_true_divide;

/* Added in release 2.5 */
 unaryfunc nb_index;
} PyNumberMethods;
</pre></div>
</div>
</dd></dl>

Binary and ternary functions may receive different kinds of arguments, depending
on the flag bit <a class="reference internal" href="#Py_TPFLAGS_CHECKTYPES" title="Py_TPFLAGS_CHECKTYPES"><tt class="xref py py-const docutils literal">Py_TPFLAGS_CHECKTYPES</tt></a>:
<ul>
<li>If <a class="reference internal" href="#Py_TPFLAGS_CHECKTYPES" title="Py_TPFLAGS_CHECKTYPES"><tt class="xref py py-const docutils literal">Py_TPFLAGS_CHECKTYPES</tt></a> is not set, the function arguments are
guaranteed to be of the object&#8217;s type; the caller is responsible for calling
the coercion method specified by the <tt class="xref py py-attr docutils literal">nb_coerce</tt> member to convert the
arguments:
<dl class="member">
<dt id="PyNumberMethods.nb_coerce">
coercion <tt class="descname">PyNumberMethods.nb_coerce</tt><a class="headerlink" href="#PyNumberMethods.nb_coerce" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="number.html#PyNumber_CoerceEx" title="PyNumber_CoerceEx"><tt class="xref c c-func docutils literal">PyNumber_CoerceEx()</tt></a> and has the same
signature. The first argument is always a pointer to an object of the
defined type. If the conversion to a common &#8220;larger&#8221; type is possible, the
function replaces the pointers with new references to the converted objects
and returns <tt class="docutils literal">0</tt>. If the conversion is not possible, the function returns
<tt class="docutils literal">1</tt>. If an error condition is set, it will return <tt class="docutils literal">-1</tt>.
</dd></dl>

</li>
<li>If the <a class="reference internal" href="#Py_TPFLAGS_CHECKTYPES" title="Py_TPFLAGS_CHECKTYPES"><tt class="xref py py-const docutils literal">Py_TPFLAGS_CHECKTYPES</tt></a> flag is set, binary and ternary
functions must check the type of all their operands, and implement the
necessary conversions (at least one of the operands is an instance of the
defined type). This is the recommended way; with Python 3 coercion will
disappear completely.
</li>
</ul>
If the operation is not defined for the given operands, binary and ternary
functions must return <tt class="docutils literal">Py_NotImplemented</tt>, if another error occurred they must
return <tt class="docutils literal">NULL</tt> and set an exception.
</div>
<div class="section" id="mapping-object-structures">
<h1>Mapping Object Structures<a class="headerlink" href="#mapping-object-structures" title="Permalink to this headline">¶</a></h1>
<dl class="type">
<dt id="PyMappingMethods">
<tt class="descname">PyMappingMethods</tt><a class="headerlink" href="#PyMappingMethods" title="Permalink to this definition">¶</a></dt>
<dd>This structure holds pointers to the functions which an object uses to
implement the mapping protocol. It has three members:
</dd></dl>

<dl class="member">
<dt id="PyMappingMethods.mp_length">
lenfunc <tt class="descname">PyMappingMethods.mp_length</tt><a class="headerlink" href="#PyMappingMethods.mp_length" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="mapping.html#PyMapping_Length" title="PyMapping_Length"><tt class="xref c c-func docutils literal">PyMapping_Length()</tt></a> and
<a class="reference internal" href="object.html#PyObject_Size" title="PyObject_Size"><tt class="xref c c-func docutils literal">PyObject_Size()</tt></a>, and has the same signature. This slot may be set to
NULL if the object has no defined length.
</dd></dl>

<dl class="member">
<dt id="PyMappingMethods.mp_subscript">
binaryfunc <tt class="descname">PyMappingMethods.mp_subscript</tt><a class="headerlink" href="#PyMappingMethods.mp_subscript" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="object.html#PyObject_GetItem" title="PyObject_GetItem"><tt class="xref c c-func docutils literal">PyObject_GetItem()</tt></a> and has the same
signature. This slot must be filled for the <a class="reference internal" href="mapping.html#PyMapping_Check" title="PyMapping_Check"><tt class="xref c c-func docutils literal">PyMapping_Check()</tt></a>
function to return <tt class="docutils literal">1</tt>, it can be NULL otherwise.
</dd></dl>

<dl class="member">
<dt id="PyMappingMethods.mp_ass_subscript">
objobjargproc <tt class="descname">PyMappingMethods.mp_ass_subscript</tt><a class="headerlink" href="#PyMappingMethods.mp_ass_subscript" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="object.html#PyObject_SetItem" title="PyObject_SetItem"><tt class="xref c c-func docutils literal">PyObject_SetItem()</tt></a> and has the same
signature. If this slot is NULL, the object does not support item
assignment.
</dd></dl>

</div>
<div class="section" id="sequence-object-structures">
<h1>Sequence Object Structures<a class="headerlink" href="#sequence-object-structures" title="Permalink to this headline">¶</a></h1>
<dl class="type">
<dt id="PySequenceMethods">
<tt class="descname">PySequenceMethods</tt><a class="headerlink" href="#PySequenceMethods" title="Permalink to this definition">¶</a></dt>
<dd>This structure holds pointers to the functions which an object uses to
implement the sequence protocol.
</dd></dl>

<dl class="member">
<dt id="PySequenceMethods.sq_length">
lenfunc <tt class="descname">PySequenceMethods.sq_length</tt><a class="headerlink" href="#PySequenceMethods.sq_length" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="sequence.html#PySequence_Size" title="PySequence_Size"><tt class="xref c c-func docutils literal">PySequence_Size()</tt></a> and <a class="reference internal" href="object.html#PyObject_Size" title="PyObject_Size"><tt class="xref c c-func docutils literal">PyObject_Size()</tt></a>,
and has the same signature.
</dd></dl>

<dl class="member">
<dt id="PySequenceMethods.sq_concat">
binaryfunc <tt class="descname">PySequenceMethods.sq_concat</tt><a class="headerlink" href="#PySequenceMethods.sq_concat" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="sequence.html#PySequence_Concat" title="PySequence_Concat"><tt class="xref c c-func docutils literal">PySequence_Concat()</tt></a> and has the same
signature. It is also used by the <tt class="docutils literal">+</tt> operator, after trying the numeric
addition via the <tt class="xref py py-attr docutils literal">tp_as_number.nb_add</tt> slot.
</dd></dl>

<dl class="member">
<dt id="PySequenceMethods.sq_repeat">
ssizeargfunc <tt class="descname">PySequenceMethods.sq_repeat</tt><a class="headerlink" href="#PySequenceMethods.sq_repeat" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="sequence.html#PySequence_Repeat" title="PySequence_Repeat"><tt class="xref c c-func docutils literal">PySequence_Repeat()</tt></a> and has the same
signature. It is also used by the <tt class="docutils literal">*</tt> operator, after trying numeric
multiplication via the <tt class="xref py py-attr docutils literal">tp_as_number.nb_mul</tt> slot.
</dd></dl>

<dl class="member">
<dt id="PySequenceMethods.sq_item">
ssizeargfunc <tt class="descname">PySequenceMethods.sq_item</tt><a class="headerlink" href="#PySequenceMethods.sq_item" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="sequence.html#PySequence_GetItem" title="PySequence_GetItem"><tt class="xref c c-func docutils literal">PySequence_GetItem()</tt></a> and has the same
signature. This slot must be filled for the <a class="reference internal" href="sequence.html#PySequence_Check" title="PySequence_Check"><tt class="xref c c-func docutils literal">PySequence_Check()</tt></a>
function to return <tt class="docutils literal">1</tt>, it can be NULL otherwise.
Negative indexes are handled as follows: if the <tt class="xref py py-attr docutils literal">sq_length</tt> slot is
filled, it is called and the sequence length is used to compute a positive
index which is passed to <tt class="xref py py-attr docutils literal">sq_item</tt>. If <tt class="xref py py-attr docutils literal">sq_length</tt> is NULL,
the index is passed as is to the function.
</dd></dl>

<dl class="member">
<dt id="PySequenceMethods.sq_ass_item">
ssizeobjargproc <tt class="descname">PySequenceMethods.sq_ass_item</tt><a class="headerlink" href="#PySequenceMethods.sq_ass_item" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="sequence.html#PySequence_SetItem" title="PySequence_SetItem"><tt class="xref c c-func docutils literal">PySequence_SetItem()</tt></a> and has the same
signature. This slot may be left to NULL if the object does not support
item assignment.
</dd></dl>

<dl class="member">
<dt id="PySequenceMethods.sq_contains">
objobjproc <tt class="descname">PySequenceMethods.sq_contains</tt><a class="headerlink" href="#PySequenceMethods.sq_contains" title="Permalink to this definition">¶</a></dt>
<dd>This function may be used by <a class="reference internal" href="sequence.html#PySequence_Contains" title="PySequence_Contains"><tt class="xref c c-func docutils literal">PySequence_Contains()</tt></a> and has the same
signature. This slot may be left to NULL, in this case
<a class="reference internal" href="sequence.html#PySequence_Contains" title="PySequence_Contains"><tt class="xref c c-func docutils literal">PySequence_Contains()</tt></a> simply traverses the sequence until it finds a
match.
</dd></dl>

<dl class="member">
<dt id="PySequenceMethods.sq_inplace_concat">
binaryfunc <tt class="descname">PySequenceMethods.sq_inplace_concat</tt><a class="headerlink" href="#PySequenceMethods.sq_inplace_concat" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="sequence.html#PySequence_InPlaceConcat" title="PySequence_InPlaceConcat"><tt class="xref c c-func docutils literal">PySequence_InPlaceConcat()</tt></a> and has the same
signature. It should modify its first operand, and return it.
</dd></dl>

<dl class="member">
<dt id="PySequenceMethods.sq_inplace_repeat">
ssizeargfunc <tt class="descname">PySequenceMethods.sq_inplace_repeat</tt><a class="headerlink" href="#PySequenceMethods.sq_inplace_repeat" title="Permalink to this definition">¶</a></dt>
<dd>This function is used by <a class="reference internal" href="sequence.html#PySequence_InPlaceRepeat" title="PySequence_InPlaceRepeat"><tt class="xref c c-func docutils literal">PySequence_InPlaceRepeat()</tt></a> and has the same
signature. It should modify its first operand, and return it.
</dd></dl>

</div>
<div class="section" id="buffer-object-structures">
<h1>Buffer Object Structures<a class="headerlink" href="#buffer-object-structures" title="Permalink to this headline">¶</a></h1>
The buffer interface exports a model where an object can expose its internal
data as a set of chunks of data, where each chunk is specified as a
pointer/length pair. These chunks are called segments and are presumed
to be non-contiguous in memory.
If an object does not export the buffer interface, then its <tt class="xref py py-attr docutils literal">tp_as_buffer</tt>
member in the <a class="reference internal" href="type.html#PyTypeObject" title="PyTypeObject"><tt class="xref c c-type docutils literal">PyTypeObject</tt></a> structure should be NULL. Otherwise, the
<tt class="xref py py-attr docutils literal">tp_as_buffer</tt> will point to a <a class="reference internal" href="#PyBufferProcs" title="PyBufferProcs"><tt class="xref c c-type docutils literal">PyBufferProcs</tt></a> structure.
<div class="admonition note">
Note
It is very important that your <a class="reference internal" href="type.html#PyTypeObject" title="PyTypeObject"><tt class="xref c c-type docutils literal">PyTypeObject</tt></a> structure uses
<a class="reference internal" href="#Py_TPFLAGS_DEFAULT" title="Py_TPFLAGS_DEFAULT"><tt class="xref py py-const docutils literal">Py_TPFLAGS_DEFAULT</tt></a> for the value of the <tt class="xref py py-attr docutils literal">tp_flags</tt> member rather
than <tt class="docutils literal">0</tt>. This tells the Python runtime that your <a class="reference internal" href="#PyBufferProcs" title="PyBufferProcs"><tt class="xref c c-type docutils literal">PyBufferProcs</tt></a>
structure contains the <tt class="xref py py-attr docutils literal">bf_getcharbuffer</tt> slot. Older versions of Python
did not have this member, so a new Python interpreter using an old extension
needs to be able to test for its presence before using it.
</div>
<dl class="type">
<dt id="PyBufferProcs">
<tt class="descname">PyBufferProcs</tt><a class="headerlink" href="#PyBufferProcs" title="Permalink to this definition">¶</a></dt>
<dd>Structure used to hold the function pointers which define an implementation of
the buffer protocol.
The first slot is <tt class="xref py py-attr docutils literal">bf_getreadbuffer</tt>, of type <tt class="xref c c-type docutils literal">getreadbufferproc</tt>.
If this slot is NULL, then the object does not support reading from the
internal data. This is non-sensical, so implementors should fill this in, but
callers should test that the slot contains a non-NULL value.
The next slot is <tt class="xref py py-attr docutils literal">bf_getwritebuffer</tt> having type
<tt class="xref c c-type docutils literal">getwritebufferproc</tt>. This slot may be NULL if the object does not
allow writing into its returned buffers.
The third slot is <tt class="xref py py-attr docutils literal">bf_getsegcount</tt>, with type <tt class="xref c c-type docutils literal">getsegcountproc</tt>.
This slot must not be NULL and is used to inform the caller how many segments
the object contains. Simple objects such as <a class="reference internal" href="string.html#PyString_Type" title="PyString_Type"><tt class="xref c c-type docutils literal">PyString_Type</tt></a> and
<a class="reference internal" href="buffer.html#PyBuffer_Type" title="PyBuffer_Type"><tt class="xref c c-type docutils literal">PyBuffer_Type</tt></a> objects contain a single segment.
The last slot is <tt class="xref py py-attr docutils literal">bf_getcharbuffer</tt>, of type <tt class="xref c c-type docutils literal">getcharbufferproc</tt>.
This slot will only be present if the <a class="reference internal" href="#Py_TPFLAGS_HAVE_GETCHARBUFFER" title="Py_TPFLAGS_HAVE_GETCHARBUFFER"><tt class="xref py py-const docutils literal">Py_TPFLAGS_HAVE_GETCHARBUFFER</tt></a>
flag is present in the <tt class="xref py py-attr docutils literal">tp_flags</tt> field of the object&#8217;s
<a class="reference internal" href="type.html#PyTypeObject" title="PyTypeObject"><tt class="xref c c-type docutils literal">PyTypeObject</tt></a>. Before using this slot, the caller should test whether it
is present by using the <a class="reference internal" href="type.html#PyType_HasFeature" title="PyType_HasFeature"><tt class="xref c c-func docutils literal">PyType_HasFeature()</tt></a> function. If the flag is
present, <tt class="xref py py-attr docutils literal">bf_getcharbuffer</tt> may be NULL, indicating that the object&#8217;s
contents cannot be used as 8-bit characters. The slot function may also raise
an error if the object&#8217;s contents cannot be interpreted as 8-bit characters.
For example, if the object is an array which is configured to hold floating
point values, an exception may be raised if a caller attempts to use
<tt class="xref py py-attr docutils literal">bf_getcharbuffer</tt> to fetch a sequence of 8-bit characters. This notion of
exporting the internal buffers as &#8220;text&#8221; is used to distinguish between objects
that are binary in nature, and those which have character-based content.
<div class="admonition note">
Note
The current policy seems to state that these characters may be multi-byte
characters. This implies that a buffer size of N does not mean there are N
characters present.
</div>
</dd></dl>

<dl class="data">
<dt>
<tt class="descname">Py_TPFLAGS_HAVE_GETCHARBUFFER</tt></dt>
<dd>Flag bit set in the type structure to indicate that the <tt class="xref py py-attr docutils literal">bf_getcharbuffer</tt>
slot is known. This being set does not indicate that the object supports the
buffer interface or that the <tt class="xref py py-attr docutils literal">bf_getcharbuffer</tt> slot is non-NULL.
</dd></dl>

<dl class="type">
<dt id="readbufferproc">
Py_ssize_t <tt class="descname">(*readbufferproc)</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>&nbsp;*self, Py_ssize_t&nbsp;segment, void&nbsp;**ptrptr<big>)</big><a class="headerlink" href="#readbufferproc" title="Permalink to this definition">¶</a></dt>
<dd>Return a pointer to a readable segment of the buffer in <tt class="docutils literal">*ptrptr</tt>. This
function is allowed to raise an exception, in which case it must return <tt class="docutils literal">-1</tt>.
The segment which is specified must be zero or positive, and strictly less
than the number of segments returned by the <tt class="xref py py-attr docutils literal">bf_getsegcount</tt> slot
function. On success, it returns the length of the segment, and sets
<tt class="docutils literal">*ptrptr</tt> to a pointer to that memory.
</dd></dl>

<dl class="type">
<dt id="writebufferproc">
Py_ssize_t <tt class="descname">(*writebufferproc)</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>&nbsp;*self, Py_ssize_t&nbsp;segment, void&nbsp;**ptrptr<big>)</big><a class="headerlink" href="#writebufferproc" title="Permalink to this definition">¶</a></dt>
<dd>Return a pointer to a writable memory buffer in <tt class="docutils literal">*ptrptr</tt>, and the length of
that segment as the function return value. The memory buffer must correspond to
buffer segment segment. Must return <tt class="docutils literal">-1</tt> and set an exception on error.
<a class="reference internal" href="../library/exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><tt class="xref py py-exc docutils literal">TypeError</tt></a> should be raised if the object only supports read-only buffers,
and <a class="reference internal" href="../library/exceptions.html#exceptions.SystemError" title="exceptions.SystemError"><tt class="xref py py-exc docutils literal">SystemError</tt></a> should be raised when segment specifies a segment that
doesn&#8217;t exist.
</dd></dl>

<dl class="type">
<dt id="segcountproc">
Py_ssize_t <tt class="descname">(*segcountproc)</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>&nbsp;*self, Py_ssize_t&nbsp;*lenp<big>)</big><a class="headerlink" href="#segcountproc" title="Permalink to this definition">¶</a></dt>
<dd>Return the number of memory segments which comprise the buffer. If lenp is
not NULL, the implementation must report the sum of the sizes (in bytes) of
all segments in <tt class="docutils literal">*lenp</tt>. The function cannot fail.
</dd></dl>

<dl class="type">
<dt id="charbufferproc">
Py_ssize_t <tt class="descname">(*charbufferproc)</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>&nbsp;*self, Py_ssize_t&nbsp;segment, const char&nbsp;**ptrptr<big>)</big><a class="headerlink" href="#charbufferproc" title="Permalink to this definition">¶</a></dt>
<dd>Return the size of the segment segment that ptrptr is set to. <tt class="docutils literal">*ptrptr</tt>
is set to the memory buffer. Returns <tt class="docutils literal">-1</tt> on error.
</dd></dl>

</div>

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<li><a class="reference internal" href="#">Type Objects</a></li>
<li><a class="reference internal" href="#number-object-structures">Number Object Structures</a></li>
<li><a class="reference internal" href="#mapping-object-structures">Mapping Object Structures</a></li>
<li><a class="reference internal" href="#sequence-object-structures">Sequence Object Structures</a></li>
<li><a class="reference internal" href="#buffer-object-structures">Buffer Object Structures</a></li>
</ul>

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