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2to3.html
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__builtin__.html
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__future__.html
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__main__.html
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abc.html
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aetools.html
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aifc.html
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al.html
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allos.html
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anydbm.html
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archiving.html
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argparse.html
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array.html
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ast.html
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atexit.html
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audioop.html
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autogil.html
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basehttpserver.html
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bastion.html
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bdb.html
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calendar.html
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carbon.html
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cd.html
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cgi.html
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cgihttpserver.html
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cgitb.html
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chunk.html
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cmd.html
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code.html
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codecs.html
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codeop.html
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collections.html
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colorpicker.html
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colorsys.html
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commands.html
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compileall.html
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compiler.html
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configparser.html
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constants.html
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contextlib.html
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cookie.html
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cookielib.html
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copy.html
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crypt.html
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crypto.html
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csv.html
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ctypes.html
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custominterp.html
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datatypes.html
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datetime.html
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dbm.html
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development.html
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dis.html
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distutils.html
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doctest.html
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dumbdbm.html
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dummy_thread.html
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dummy_threading.html
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easydialogs.html
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email-examples.html
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email.charset.html
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email.encoders.html
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email.generator.html
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email.html
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fpformat.html
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fractions.html
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framework.html
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frameworks.html
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ftplib.html
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functions.html
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functools.html
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future_builtins.html
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gc.html
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gdbm.html
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gensuitemodule.html
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getopt.html
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getpass.html
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gettext.html
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gl.html
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glob.html
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grp.html
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gzip.html
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hashlib.html
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heapq.html
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hmac.html
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hotshot.html
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htmllib.html
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htmlparser.html
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httplib.html
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i18n.html
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ic.html
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idle.html
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imageop.html
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imaplib.html
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imgfile.html
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imghdr.html
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imp.html
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importlib.html
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imputil.html
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index.html
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inspect.html
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internet.html
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intro.html
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io.html
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ipc.html
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itertools.html
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jpeg.html
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json.html
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keyword.html
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language.html
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linecache.html
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locale.html
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logging.config.html
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logging.handlers.html
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logging.html
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mac.html
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macostools.html
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macpath.html
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mailbox.html
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mailcap.html
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markup.html
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math.html
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md5.html
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mmap.html
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modulefinder.html
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modules.html
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msilib.html
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msvcrt.html
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multiprocessing.html
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mutex.html
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netdata.html
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netrc.html
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new.html
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nis.html
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nntplib.html
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numbers.html
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numeric.html
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othergui.html
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pdb.html
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pickle.html
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pkgutil.html
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profile.html
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python.html
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random.html
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readline.html
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zipimport.html
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zlib.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>15.2. io — Core tools for working with streams — Python 2.7.5 documentation</title> <link rel="stylesheet" href="../_static/default.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '2.7.5', COLLAPSE_INDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.5 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="top" title="Python 2.7.5 documentation" href="../index.html" /> <link rel="up" title="15. 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Generic Operating System Services</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-io"> <span id="io-core-tools-for-working-with-streams"></span><h1>15.2. <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><tt class="xref py py-mod docutils literal"><span class="pre">io</span></tt></a> — Core tools for working with streams<a class="headerlink" href="#module-io" title="Permalink to this headline">¶</a></h1> <p class="versionadded"> <span class="versionmodified">New in version 2.6.</span></p> <p>The <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><tt class="xref py py-mod docutils literal"><span class="pre">io</span></tt></a> module provides the Python interfaces to stream handling. Under Python 2.x, this is proposed as an alternative to the built-in <a class="reference internal" href="functions.html#file" title="file"><tt class="xref py py-class docutils literal"><span class="pre">file</span></tt></a> object, but in Python 3.x it is the default interface to access files and streams.</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">Since this module has been designed primarily for Python 3.x, you have to be aware that all uses of “bytes” in this document refer to the <a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a> type (of which <tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt> is an alias), and all uses of “text” refer to the <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> type. Furthermore, those two types are not interchangeable in the <a class="reference internal" href="#module-io" title="io: Core tools for working with streams."><tt class="xref py py-mod docutils literal"><span class="pre">io</span></tt></a> APIs.</p> </div> <p>At the top of the I/O hierarchy is the abstract base class <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>. It defines the basic interface to a stream. Note, however, that there is no separation between reading and writing to streams; implementations are allowed to raise an <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> if they do not support a given operation.</p> <p>Extending <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> is <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> which deals simply with the reading and writing of raw bytes to a stream. <a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> subclasses <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> to provide an interface to files in the machine’s file system.</p> <p><a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> deals with buffering on a raw byte stream (<a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a>). Its subclasses, <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a>, <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a>, and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a> buffer streams that are readable, writable, and both readable and writable. <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> provides a buffered interface to random access streams. <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a> is a simple stream of in-memory bytes.</p> <p>Another <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> subclass, <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a>, deals with streams whose bytes represent text, and handles encoding and decoding from and to <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> strings. <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a>, which extends it, is a buffered text interface to a buffered raw stream (<a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>). Finally, <a class="reference internal" href="stringio.html#module-StringIO" title="StringIO: Read and write strings as if they were files."><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> is an in-memory stream for unicode text.</p> <p>Argument names are not part of the specification, and only the arguments of <a class="reference internal" href="#io.open" title="io.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> are intended to be used as keyword arguments.</p> <div class="section" id="module-interface"> <h2>15.2.1. Module Interface<a class="headerlink" href="#module-interface" title="Permalink to this headline">¶</a></h2> <dl class="data"> <dt id="io.DEFAULT_BUFFER_SIZE"> <tt class="descclassname">io.</tt><tt class="descname">DEFAULT_BUFFER_SIZE</tt><a class="headerlink" href="#io.DEFAULT_BUFFER_SIZE" title="Permalink to this definition">¶</a></dt> <dd><p>An int containing the default buffer size used by the module’s buffered I/O classes. <a class="reference internal" href="#io.open" title="io.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> uses the file’s blksize (as obtained by <a class="reference internal" href="os.html#os.stat" title="os.stat"><tt class="xref py py-func docutils literal"><span class="pre">os.stat()</span></tt></a>) if possible.</p> </dd></dl> <dl class="function"> <dt id="io.open"> <tt class="descclassname">io.</tt><tt class="descname">open</tt><big>(</big><em>file</em>, <em>mode='r'</em>, <em>buffering=-1</em>, <em>encoding=None</em>, <em>errors=None</em>, <em>newline=None</em>, <em>closefd=True</em><big>)</big><a class="headerlink" href="#io.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open <em>file</em> and return a corresponding stream. If the file cannot be opened, an <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> is raised.</p> <p><em>file</em> is either a string giving the pathname (absolute or relative to the current working directory) of the file to be opened or an integer file descriptor of the file to be wrapped. (If a file descriptor is given, it is closed when the returned I/O object is closed, unless <em>closefd</em> is set to <tt class="docutils literal"><span class="pre">False</span></tt>.)</p> <p><em>mode</em> is an optional string that specifies the mode in which the file is opened. It defaults to <tt class="docutils literal"><span class="pre">'r'</span></tt> which means open for reading in text mode. Other common values are <tt class="docutils literal"><span class="pre">'w'</span></tt> for writing (truncating the file if it already exists), and <tt class="docutils literal"><span class="pre">'a'</span></tt> for appending (which on <em>some</em> Unix systems, means that <em>all</em> writes append to the end of the file regardless of the current seek position). In text mode, if <em>encoding</em> is not specified the encoding used is platform dependent. (For reading and writing raw bytes use binary mode and leave <em>encoding</em> unspecified.) The available modes are:</p> <table border="1" class="docutils"> <colgroup> <col width="13%" /> <col width="88%" /> </colgroup> <tbody valign="top"> <tr class="row-odd"><td>Character</td> <td>Meaning</td> </tr> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">'r'</span></tt></td> <td>open for reading (default)</td> </tr> <tr class="row-odd"><td><tt class="docutils literal"><span class="pre">'w'</span></tt></td> <td>open for writing, truncating the file first</td> </tr> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">'a'</span></tt></td> <td>open for writing, appending to the end of the file if it exists</td> </tr> <tr class="row-odd"><td><tt class="docutils literal"><span class="pre">'b'</span></tt></td> <td>binary mode</td> </tr> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">'t'</span></tt></td> <td>text mode (default)</td> </tr> <tr class="row-odd"><td><tt class="docutils literal"><span class="pre">'+'</span></tt></td> <td>open a disk file for updating (reading and writing)</td> </tr> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">'U'</span></tt></td> <td>universal newlines mode (for backwards compatibility; should not be used in new code)</td> </tr> </tbody> </table> <p>The default mode is <tt class="docutils literal"><span class="pre">'rt'</span></tt> (open for reading text). For binary random access, the mode <tt class="docutils literal"><span class="pre">'w+b'</span></tt> opens and truncates the file to 0 bytes, while <tt class="docutils literal"><span class="pre">'r+b'</span></tt> opens the file without truncation.</p> <p>Python distinguishes between files opened in binary and text modes, even when the underlying operating system doesn’t. Files opened in binary mode (including <tt class="docutils literal"><span class="pre">'b'</span></tt> in the <em>mode</em> argument) return contents as <tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt> objects without any decoding. In text mode (the default, or when <tt class="docutils literal"><span class="pre">'t'</span></tt> is included in the <em>mode</em> argument), the contents of the file are returned as <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> strings, the bytes having been first decoded using a platform-dependent encoding or using the specified <em>encoding</em> if given.</p> <p><em>buffering</em> is an optional integer used to set the buffering policy. Pass 0 to switch buffering off (only allowed in binary mode), 1 to select line buffering (only usable in text mode), and an integer > 1 to indicate the size of a fixed-size chunk buffer. When no <em>buffering</em> argument is given, the default buffering policy works as follows:</p> <ul class="simple"> <li>Binary files are buffered in fixed-size chunks; the size of the buffer is chosen using a heuristic trying to determine the underlying device’s “block size” and falling back on <a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><tt class="xref py py-attr docutils literal"><span class="pre">DEFAULT_BUFFER_SIZE</span></tt></a>. On many systems, the buffer will typically be 4096 or 8192 bytes long.</li> <li>“Interactive” text files (files for which <tt class="xref py py-meth docutils literal"><span class="pre">isatty()</span></tt> returns True) use line buffering. Other text files use the policy described above for binary files.</li> </ul> <p><em>encoding</em> is the name of the encoding used to decode or encode the file. This should only be used in text mode. The default encoding is platform dependent (whatever <a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><tt class="xref py py-func docutils literal"><span class="pre">locale.getpreferredencoding()</span></tt></a> returns), but any encoding supported by Python can be used. See the <a class="reference internal" href="codecs.html#module-codecs" title="codecs: Encode and decode data and streams."><tt class="xref py py-mod docutils literal"><span class="pre">codecs</span></tt></a> module for the list of supported encodings.</p> <p><em>errors</em> is an optional string that specifies how encoding and decoding errors are to be handled–this cannot be used in binary mode. Pass <tt class="docutils literal"><span class="pre">'strict'</span></tt> to raise a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> exception if there is an encoding error (the default of <tt class="docutils literal"><span class="pre">None</span></tt> has the same effect), or pass <tt class="docutils literal"><span class="pre">'ignore'</span></tt> to ignore errors. (Note that ignoring encoding errors can lead to data loss.) <tt class="docutils literal"><span class="pre">'replace'</span></tt> causes a replacement marker (such as <tt class="docutils literal"><span class="pre">'?'</span></tt>) to be inserted where there is malformed data. When writing, <tt class="docutils literal"><span class="pre">'xmlcharrefreplace'</span></tt> (replace with the appropriate XML character reference) or <tt class="docutils literal"><span class="pre">'backslashreplace'</span></tt> (replace with backslashed escape sequences) can be used. Any other error handling name that has been registered with <a class="reference internal" href="codecs.html#codecs.register_error" title="codecs.register_error"><tt class="xref py py-func docutils literal"><span class="pre">codecs.register_error()</span></tt></a> is also valid.</p> <p id="index-0"><em>newline</em> controls how <a class="reference internal" href="../glossary.html#term-universal-newlines"><em class="xref std std-term">universal newlines</em></a> works (it only applies to text mode). It can be <tt class="docutils literal"><span class="pre">None</span></tt>, <tt class="docutils literal"><span class="pre">''</span></tt>, <tt class="docutils literal"><span class="pre">'\n'</span></tt>, <tt class="docutils literal"><span class="pre">'\r'</span></tt>, and <tt class="docutils literal"><span class="pre">'\r\n'</span></tt>. It works as follows:</p> <ul class="simple"> <li>On input, if <em>newline</em> is <tt class="docutils literal"><span class="pre">None</span></tt>, universal newlines mode is enabled. Lines in the input can end in <tt class="docutils literal"><span class="pre">'\n'</span></tt>, <tt class="docutils literal"><span class="pre">'\r'</span></tt>, or <tt class="docutils literal"><span class="pre">'\r\n'</span></tt>, and these are translated into <tt class="docutils literal"><span class="pre">'\n'</span></tt> before being returned to the caller. If it is <tt class="docutils literal"><span class="pre">''</span></tt>, universal newlines mode is enabled, but line endings are returned to the caller untranslated. If it has any of the other legal values, input lines are only terminated by the given string, and the line ending is returned to the caller untranslated.</li> <li>On output, if <em>newline</em> is <tt class="docutils literal"><span class="pre">None</span></tt>, any <tt class="docutils literal"><span class="pre">'\n'</span></tt> characters written are translated to the system default line separator, <a class="reference internal" href="os.html#os.linesep" title="os.linesep"><tt class="xref py py-data docutils literal"><span class="pre">os.linesep</span></tt></a>. If <em>newline</em> is <tt class="docutils literal"><span class="pre">''</span></tt>, no translation takes place. If <em>newline</em> is any of the other legal values, any <tt class="docutils literal"><span class="pre">'\n'</span></tt> characters written are translated to the given string.</li> </ul> <p>If <em>closefd</em> is <tt class="docutils literal"><span class="pre">False</span></tt> and a file descriptor rather than a filename was given, the underlying file descriptor will be kept open when the file is closed. If a filename is given <em>closefd</em> has no effect and must be <tt class="docutils literal"><span class="pre">True</span></tt> (the default).</p> <p>The type of file object returned by the <a class="reference internal" href="#io.open" title="io.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> function depends on the mode. When <a class="reference internal" href="#io.open" title="io.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> is used to open a file in a text mode (<tt class="docutils literal"><span class="pre">'w'</span></tt>, <tt class="docutils literal"><span class="pre">'r'</span></tt>, <tt class="docutils literal"><span class="pre">'wt'</span></tt>, <tt class="docutils literal"><span class="pre">'rt'</span></tt>, etc.), it returns a subclass of <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> (specifically <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a>). When used to open a file in a binary mode with buffering, the returned class is a subclass of <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>. The exact class varies: in read binary mode, it returns a <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a>; in write binary and append binary modes, it returns a <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a>, and in read/write mode, it returns a <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a>. When buffering is disabled, the raw stream, a subclass of <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a>, <a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a>, is returned.</p> <p>It is also possible to use an <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> or <tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt> string as a file for both reading and writing. For <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> strings <a class="reference internal" href="stringio.html#module-StringIO" title="StringIO: Read and write strings as if they were files."><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> can be used like a file opened in text mode, and for <tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt> a <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a> can be used like a file opened in a binary mode.</p> </dd></dl> <dl class="exception"> <dt id="io.BlockingIOError"> <em class="property">exception </em><tt class="descclassname">io.</tt><tt class="descname">BlockingIOError</tt><a class="headerlink" href="#io.BlockingIOError" title="Permalink to this definition">¶</a></dt> <dd><p>Error raised when blocking would occur on a non-blocking stream. It inherits <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>.</p> <p>In addition to those of <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>, <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> has one attribute:</p> <dl class="attribute"> <dt id="io.BlockingIOError.characters_written"> <tt class="descname">characters_written</tt><a class="headerlink" href="#io.BlockingIOError.characters_written" title="Permalink to this definition">¶</a></dt> <dd><p>An integer containing the number of characters written to the stream before it blocked.</p> </dd></dl> </dd></dl> <dl class="exception"> <dt id="io.UnsupportedOperation"> <em class="property">exception </em><tt class="descclassname">io.</tt><tt class="descname">UnsupportedOperation</tt><a class="headerlink" href="#io.UnsupportedOperation" title="Permalink to this definition">¶</a></dt> <dd><p>An exception inheriting <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> and <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> that is raised when an unsupported operation is called on a stream.</p> </dd></dl> </div> <div class="section" id="i-o-base-classes"> <h2>15.2.2. I/O Base Classes<a class="headerlink" href="#i-o-base-classes" title="Permalink to this headline">¶</a></h2> <dl class="class"> <dt id="io.IOBase"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">IOBase</tt><a class="headerlink" href="#io.IOBase" title="Permalink to this definition">¶</a></dt> <dd><p>The abstract base class for all I/O classes, acting on streams of bytes. There is no public constructor.</p> <p>This class provides empty abstract implementations for many methods that derived classes can override selectively; the default implementations represent a file that cannot be read, written or seeked.</p> <p>Even though <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> does not declare <tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt>, or <tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt> because their signatures will vary, implementations and clients should consider those methods part of the interface. Also, implementations may raise a <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> when operations they do not support are called.</p> <p>The basic type used for binary data read from or written to a file is <tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt> (also known as <a class="reference internal" href="functions.html#str" title="str"><tt class="xref py py-class docutils literal"><span class="pre">str</span></tt></a>). <a class="reference internal" href="functions.html#bytearray" title="bytearray"><tt class="xref py py-class docutils literal"><span class="pre">bytearray</span></tt></a>s are accepted too, and in some cases (such as <tt class="xref py py-class docutils literal"><span class="pre">readinto</span></tt>) required. Text I/O classes work with <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> data.</p> <p>Note that calling any method (even inquiries) on a closed stream is undefined. Implementations may raise <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> in this case.</p> <p>IOBase (and its subclasses) support the iterator protocol, meaning that an <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> object can be iterated over yielding the lines in a stream. Lines are defined slightly differently depending on whether the stream is a binary stream (yielding <tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt>), or a text stream (yielding <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> strings). See <a class="reference internal" href="#io.IOBase.readline" title="io.IOBase.readline"><tt class="xref py py-meth docutils literal"><span class="pre">readline()</span></tt></a> below.</p> <p>IOBase is also a context manager and therefore supports the <a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement. In this example, <em>file</em> is closed after the <a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement’s suite is finished—even if an exception occurs:</p> <div class="highlight-python"><div class="highlight"><pre><span class="k">with</span> <span class="n">io</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">'spam.txt'</span><span class="p">,</span> <span class="s">'w'</span><span class="p">)</span> <span class="k">as</span> <span class="nb">file</span><span class="p">:</span> <span class="nb">file</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">u'Spam and eggs!'</span><span class="p">)</span> </pre></div> </div> <p><a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> provides these data attributes and methods:</p> <dl class="method"> <dt id="io.IOBase.close"> <tt class="descname">close</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.close" title="Permalink to this definition">¶</a></dt> <dd><p>Flush and close this stream. This method has no effect if the file is already closed. Once the file is closed, any operation on the file (e.g. reading or writing) will raise a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a>.</p> <p>As a convenience, it is allowed to call this method more than once; only the first call, however, will have an effect.</p> </dd></dl> <dl class="attribute"> <dt id="io.IOBase.closed"> <tt class="descname">closed</tt><a class="headerlink" href="#io.IOBase.closed" title="Permalink to this definition">¶</a></dt> <dd><p>True if the stream is closed.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.fileno"> <tt class="descname">fileno</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.fileno" title="Permalink to this definition">¶</a></dt> <dd><p>Return the underlying file descriptor (an integer) of the stream if it exists. An <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> is raised if the IO object does not use a file descriptor.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.flush"> <tt class="descname">flush</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.flush" title="Permalink to this definition">¶</a></dt> <dd><p>Flush the write buffers of the stream if applicable. This does nothing for read-only and non-blocking streams.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.isatty"> <tt class="descname">isatty</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.isatty" title="Permalink to this definition">¶</a></dt> <dd><p>Return <tt class="docutils literal"><span class="pre">True</span></tt> if the stream is interactive (i.e., connected to a terminal/tty device).</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.readable"> <tt class="descname">readable</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.readable" title="Permalink to this definition">¶</a></dt> <dd><p>Return <tt class="docutils literal"><span class="pre">True</span></tt> if the stream can be read from. If False, <tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt> will raise <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.readline"> <tt class="descname">readline</tt><big>(</big><em>limit=-1</em><big>)</big><a class="headerlink" href="#io.IOBase.readline" title="Permalink to this definition">¶</a></dt> <dd><p>Read and return one line from the stream. If <em>limit</em> is specified, at most <em>limit</em> bytes will be read.</p> <p>The line terminator is always <tt class="docutils literal"><span class="pre">b'\n'</span></tt> for binary files; for text files, the <em>newlines</em> argument to <a class="reference internal" href="#io.open" title="io.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> can be used to select the line terminator(s) recognized.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.readlines"> <tt class="descname">readlines</tt><big>(</big><em>hint=-1</em><big>)</big><a class="headerlink" href="#io.IOBase.readlines" title="Permalink to this definition">¶</a></dt> <dd><p>Read and return a list of lines from the stream. <em>hint</em> can be specified to control the number of lines read: no more lines will be read if the total size (in bytes/characters) of all lines so far exceeds <em>hint</em>.</p> <p>Note that it’s already possible to iterate on file objects using <tt class="docutils literal"><span class="pre">for</span> <span class="pre">line</span> <span class="pre">in</span> <span class="pre">file:</span> <span class="pre">...</span></tt> without calling <tt class="docutils literal"><span class="pre">file.readlines()</span></tt>.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.seek"> <tt class="descname">seek</tt><big>(</big><em>offset</em>, <em>whence=SEEK_SET</em><big>)</big><a class="headerlink" href="#io.IOBase.seek" title="Permalink to this definition">¶</a></dt> <dd><p>Change the stream position to the given byte <em>offset</em>. <em>offset</em> is interpreted relative to the position indicated by <em>whence</em>. Values for <em>whence</em> are:</p> <ul class="simple"> <li><tt class="xref py py-data docutils literal"><span class="pre">SEEK_SET</span></tt> or <tt class="docutils literal"><span class="pre">0</span></tt> – start of the stream (the default); <em>offset</em> should be zero or positive</li> <li><tt class="xref py py-data docutils literal"><span class="pre">SEEK_CUR</span></tt> or <tt class="docutils literal"><span class="pre">1</span></tt> – current stream position; <em>offset</em> may be negative</li> <li><tt class="xref py py-data docutils literal"><span class="pre">SEEK_END</span></tt> or <tt class="docutils literal"><span class="pre">2</span></tt> – end of the stream; <em>offset</em> is usually negative</li> </ul> <p>Return the new absolute position.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.7: </span>The <tt class="docutils literal"><span class="pre">SEEK_*</span></tt> constants</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.seekable"> <tt class="descname">seekable</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.seekable" title="Permalink to this definition">¶</a></dt> <dd><p>Return <tt class="docutils literal"><span class="pre">True</span></tt> if the stream supports random access. If <tt class="docutils literal"><span class="pre">False</span></tt>, <a class="reference internal" href="#io.IOBase.seek" title="io.IOBase.seek"><tt class="xref py py-meth docutils literal"><span class="pre">seek()</span></tt></a>, <a class="reference internal" href="#io.IOBase.tell" title="io.IOBase.tell"><tt class="xref py py-meth docutils literal"><span class="pre">tell()</span></tt></a> and <a class="reference internal" href="#io.IOBase.truncate" title="io.IOBase.truncate"><tt class="xref py py-meth docutils literal"><span class="pre">truncate()</span></tt></a> will raise <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.tell"> <tt class="descname">tell</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.tell" title="Permalink to this definition">¶</a></dt> <dd><p>Return the current stream position.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.truncate"> <tt class="descname">truncate</tt><big>(</big><em>size=None</em><big>)</big><a class="headerlink" href="#io.IOBase.truncate" title="Permalink to this definition">¶</a></dt> <dd><p>Resize the stream to the given <em>size</em> in bytes (or the current position if <em>size</em> is not specified). The current stream position isn’t changed. This resizing can extend or reduce the current file size. In case of extension, the contents of the new file area depend on the platform (on most systems, additional bytes are zero-filled, on Windows they’re undetermined). The new file size is returned.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.writable"> <tt class="descname">writable</tt><big>(</big><big>)</big><a class="headerlink" href="#io.IOBase.writable" title="Permalink to this definition">¶</a></dt> <dd><p>Return <tt class="docutils literal"><span class="pre">True</span></tt> if the stream supports writing. If <tt class="docutils literal"><span class="pre">False</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt> and <a class="reference internal" href="#io.IOBase.truncate" title="io.IOBase.truncate"><tt class="xref py py-meth docutils literal"><span class="pre">truncate()</span></tt></a> will raise <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a>.</p> </dd></dl> <dl class="method"> <dt id="io.IOBase.writelines"> <tt class="descname">writelines</tt><big>(</big><em>lines</em><big>)</big><a class="headerlink" href="#io.IOBase.writelines" title="Permalink to this definition">¶</a></dt> <dd><p>Write a list of lines to the stream. Line separators are not added, so it is usual for each of the lines provided to have a line separator at the end.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="io.RawIOBase"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">RawIOBase</tt><a class="headerlink" href="#io.RawIOBase" title="Permalink to this definition">¶</a></dt> <dd><p>Base class for raw binary I/O. It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>. There is no public constructor.</p> <p>Raw binary I/O typically provides low-level access to an underlying OS device or API, and does not try to encapsulate it in high-level primitives (this is left to Buffered I/O and Text I/O, described later in this page).</p> <p>In addition to the attributes and methods from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>, RawIOBase provides the following methods:</p> <dl class="method"> <dt id="io.RawIOBase.read"> <tt class="descname">read</tt><big>(</big><em>n=-1</em><big>)</big><a class="headerlink" href="#io.RawIOBase.read" title="Permalink to this definition">¶</a></dt> <dd><p>Read up to <em>n</em> bytes from the object and return them. As a convenience, if <em>n</em> is unspecified or -1, <a class="reference internal" href="#io.RawIOBase.readall" title="io.RawIOBase.readall"><tt class="xref py py-meth docutils literal"><span class="pre">readall()</span></tt></a> is called. Otherwise, only one system call is ever made. Fewer than <em>n</em> bytes may be returned if the operating system call returns fewer than <em>n</em> bytes.</p> <p>If 0 bytes are returned, and <em>n</em> was not 0, this indicates end of file. If the object is in non-blocking mode and no bytes are available, <tt class="docutils literal"><span class="pre">None</span></tt> is returned.</p> </dd></dl> <dl class="method"> <dt id="io.RawIOBase.readall"> <tt class="descname">readall</tt><big>(</big><big>)</big><a class="headerlink" href="#io.RawIOBase.readall" title="Permalink to this definition">¶</a></dt> <dd><p>Read and return all the bytes from the stream until EOF, using multiple calls to the stream if necessary.</p> </dd></dl> <dl class="method"> <dt id="io.RawIOBase.readinto"> <tt class="descname">readinto</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.RawIOBase.readinto" title="Permalink to this definition">¶</a></dt> <dd><p>Read up to len(b) bytes into bytearray <em>b</em> and return the number of bytes read. If the object is in non-blocking mode and no bytes are available, <tt class="docutils literal"><span class="pre">None</span></tt> is returned.</p> </dd></dl> <dl class="method"> <dt id="io.RawIOBase.write"> <tt class="descname">write</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.RawIOBase.write" title="Permalink to this definition">¶</a></dt> <dd><p>Write the given bytes or bytearray object, <em>b</em>, to the underlying raw stream and return the number of bytes written. This can be less than <tt class="docutils literal"><span class="pre">len(b)</span></tt>, depending on specifics of the underlying raw stream, and especially if it is in non-blocking mode. <tt class="docutils literal"><span class="pre">None</span></tt> is returned if the raw stream is set not to block and no single byte could be readily written to it.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="io.BufferedIOBase"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedIOBase</tt><a class="headerlink" href="#io.BufferedIOBase" title="Permalink to this definition">¶</a></dt> <dd><p>Base class for binary streams that support some kind of buffering. It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>. There is no public constructor.</p> <p>The main difference with <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> is that methods <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a>, <a class="reference internal" href="#io.BufferedIOBase.readinto" title="io.BufferedIOBase.readinto"><tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt></a> and <a class="reference internal" href="#io.BufferedIOBase.write" title="io.BufferedIOBase.write"><tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt></a> will try (respectively) to read as much input as requested or to consume all given output, at the expense of making perhaps more than one system call.</p> <p>In addition, those methods can raise <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> if the underlying raw stream is in non-blocking mode and cannot take or give enough data; unlike their <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> counterparts, they will never return <tt class="docutils literal"><span class="pre">None</span></tt>.</p> <p>Besides, the <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a> method does not have a default implementation that defers to <a class="reference internal" href="#io.BufferedIOBase.readinto" title="io.BufferedIOBase.readinto"><tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt></a>.</p> <p>A typical <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> implementation should not inherit from a <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> implementation, but wrap one, like <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> and <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> do.</p> <p><a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> provides or overrides these methods and attribute in addition to those from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p> <dl class="attribute"> <dt id="io.BufferedIOBase.raw"> <tt class="descname">raw</tt><a class="headerlink" href="#io.BufferedIOBase.raw" title="Permalink to this definition">¶</a></dt> <dd><p>The underlying raw stream (a <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> instance) that <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> deals with. This is not part of the <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> API and may not exist on some implementations.</p> </dd></dl> <dl class="method"> <dt id="io.BufferedIOBase.detach"> <tt class="descname">detach</tt><big>(</big><big>)</big><a class="headerlink" href="#io.BufferedIOBase.detach" title="Permalink to this definition">¶</a></dt> <dd><p>Separate the underlying raw stream from the buffer and return it.</p> <p>After the raw stream has been detached, the buffer is in an unusable state.</p> <p>Some buffers, like <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a>, do not have the concept of a single raw stream to return from this method. They raise <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><tt class="xref py py-exc docutils literal"><span class="pre">UnsupportedOperation</span></tt></a>.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.7.</span></p> </dd></dl> <dl class="method"> <dt id="io.BufferedIOBase.read"> <tt class="descname">read</tt><big>(</big><em>n=-1</em><big>)</big><a class="headerlink" href="#io.BufferedIOBase.read" title="Permalink to this definition">¶</a></dt> <dd><p>Read and return up to <em>n</em> bytes. If the argument is omitted, <tt class="docutils literal"><span class="pre">None</span></tt>, or negative, data is read and returned until EOF is reached. An empty bytes object is returned if the stream is already at EOF.</p> <p>If the argument is positive, and the underlying raw stream is not interactive, multiple raw reads may be issued to satisfy the byte count (unless EOF is reached first). But for interactive raw streams, at most one raw read will be issued, and a short result does not imply that EOF is imminent.</p> <p>A <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> is raised if the underlying raw stream is in non blocking-mode, and has no data available at the moment.</p> </dd></dl> <dl class="method"> <dt id="io.BufferedIOBase.read1"> <tt class="descname">read1</tt><big>(</big><em>n=-1</em><big>)</big><a class="headerlink" href="#io.BufferedIOBase.read1" title="Permalink to this definition">¶</a></dt> <dd><p>Read and return up to <em>n</em> bytes, with at most one call to the underlying raw stream’s <a class="reference internal" href="#io.RawIOBase.read" title="io.RawIOBase.read"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a> method. This can be useful if you are implementing your own buffering on top of a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> object.</p> </dd></dl> <dl class="method"> <dt id="io.BufferedIOBase.readinto"> <tt class="descname">readinto</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.BufferedIOBase.readinto" title="Permalink to this definition">¶</a></dt> <dd><p>Read up to len(b) bytes into bytearray <em>b</em> and return the number of bytes read.</p> <p>Like <a class="reference internal" href="#io.BufferedIOBase.read" title="io.BufferedIOBase.read"><tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt></a>, multiple reads may be issued to the underlying raw stream, unless the latter is ‘interactive’.</p> <p>A <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> is raised if the underlying raw stream is in non blocking-mode, and has no data available at the moment.</p> </dd></dl> <dl class="method"> <dt id="io.BufferedIOBase.write"> <tt class="descname">write</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.BufferedIOBase.write" title="Permalink to this definition">¶</a></dt> <dd><p>Write the given bytes or bytearray object, <em>b</em> and return the number of bytes written (never less than <tt class="docutils literal"><span class="pre">len(b)</span></tt>, since if the write fails an <a class="reference internal" href="exceptions.html#exceptions.IOError" title="exceptions.IOError"><tt class="xref py py-exc docutils literal"><span class="pre">IOError</span></tt></a> will be raised). Depending on the actual implementation, these bytes may be readily written to the underlying stream, or held in a buffer for performance and latency reasons.</p> <p>When in non-blocking mode, a <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> is raised if the data needed to be written to the raw stream but it couldn’t accept all the data without blocking.</p> </dd></dl> </dd></dl> </div> <div class="section" id="raw-file-i-o"> <h2>15.2.3. Raw File I/O<a class="headerlink" href="#raw-file-i-o" title="Permalink to this headline">¶</a></h2> <dl class="class"> <dt id="io.FileIO"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">FileIO</tt><big>(</big><em>name</em>, <em>mode='r'</em>, <em>closefd=True</em><big>)</big><a class="headerlink" href="#io.FileIO" title="Permalink to this definition">¶</a></dt> <dd><p><a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> represents an OS-level file containing bytes data. It implements the <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> interface (and therefore the <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> interface, too).</p> <p>The <em>name</em> can be one of two things:</p> <ul class="simple"> <li>a string representing the path to the file which will be opened;</li> <li>an integer representing the number of an existing OS-level file descriptor to which the resulting <a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> object will give access.</li> </ul> <p>The <em>mode</em> can be <tt class="docutils literal"><span class="pre">'r'</span></tt>, <tt class="docutils literal"><span class="pre">'w'</span></tt> or <tt class="docutils literal"><span class="pre">'a'</span></tt> for reading (default), writing, or appending. The file will be created if it doesn’t exist when opened for writing or appending; it will be truncated when opened for writing. Add a <tt class="docutils literal"><span class="pre">'+'</span></tt> to the mode to allow simultaneous reading and writing.</p> <p>The <tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt> (when called with a positive argument), <tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">write()</span></tt> methods on this class will only make one system call.</p> <p>In addition to the attributes and methods from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a> and <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a>, <a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> provides the following data attributes and methods:</p> <dl class="attribute"> <dt id="io.FileIO.mode"> <tt class="descname">mode</tt><a class="headerlink" href="#io.FileIO.mode" title="Permalink to this definition">¶</a></dt> <dd><p>The mode as given in the constructor.</p> </dd></dl> <dl class="attribute"> <dt id="io.FileIO.name"> <tt class="descname">name</tt><a class="headerlink" href="#io.FileIO.name" title="Permalink to this definition">¶</a></dt> <dd><p>The file name. This is the file descriptor of the file when no name is given in the constructor.</p> </dd></dl> </dd></dl> </div> <div class="section" id="buffered-streams"> <h2>15.2.4. Buffered Streams<a class="headerlink" href="#buffered-streams" title="Permalink to this headline">¶</a></h2> <p>Buffered I/O streams provide a higher-level interface to an I/O device than raw I/O does.</p> <dl class="class"> <dt id="io.BytesIO"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BytesIO</tt><big>(</big><span class="optional">[</span><em>initial_bytes</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#io.BytesIO" title="Permalink to this definition">¶</a></dt> <dd><p>A stream implementation using an in-memory bytes buffer. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>.</p> <p>The argument <em>initial_bytes</em> is an optional initial <tt class="xref py py-class docutils literal"><span class="pre">bytes</span></tt>.</p> <p><a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a> provides or overrides these methods in addition to those from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p> <dl class="method"> <dt id="io.BytesIO.getvalue"> <tt class="descname">getvalue</tt><big>(</big><big>)</big><a class="headerlink" href="#io.BytesIO.getvalue" title="Permalink to this definition">¶</a></dt> <dd><p>Return <tt class="docutils literal"><span class="pre">bytes</span></tt> containing the entire contents of the buffer.</p> </dd></dl> <dl class="method"> <dt id="io.BytesIO.read1"> <tt class="descname">read1</tt><big>(</big><big>)</big><a class="headerlink" href="#io.BytesIO.read1" title="Permalink to this definition">¶</a></dt> <dd><p>In <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a>, this is the same as <tt class="xref py py-meth docutils literal"><span class="pre">read()</span></tt>.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="io.BufferedReader"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedReader</tt><big>(</big><em>raw</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><big>)</big><a class="headerlink" href="#io.BufferedReader" title="Permalink to this definition">¶</a></dt> <dd><p>A buffer providing higher-level access to a readable, sequential <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> object. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>. When reading data from this object, a larger amount of data may be requested from the underlying raw stream, and kept in an internal buffer. The buffered data can then be returned directly on subsequent reads.</p> <p>The constructor creates a <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> for the given readable <em>raw</em> stream and <em>buffer_size</em>. If <em>buffer_size</em> is omitted, <a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><tt class="xref py py-data docutils literal"><span class="pre">DEFAULT_BUFFER_SIZE</span></tt></a> is used.</p> <p><a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> provides or overrides these methods in addition to those from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p> <dl class="method"> <dt id="io.BufferedReader.peek"> <tt class="descname">peek</tt><big>(</big><span class="optional">[</span><em>n</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#io.BufferedReader.peek" title="Permalink to this definition">¶</a></dt> <dd><p>Return bytes from the stream without advancing the position. At most one single read on the raw stream is done to satisfy the call. The number of bytes returned may be less or more than requested.</p> </dd></dl> <dl class="method"> <dt id="io.BufferedReader.read"> <tt class="descname">read</tt><big>(</big><span class="optional">[</span><em>n</em><span class="optional">]</span><big>)</big><a class="headerlink" href="#io.BufferedReader.read" title="Permalink to this definition">¶</a></dt> <dd><p>Read and return <em>n</em> bytes, or if <em>n</em> is not given or negative, until EOF or if the read call would block in non-blocking mode.</p> </dd></dl> <dl class="method"> <dt id="io.BufferedReader.read1"> <tt class="descname">read1</tt><big>(</big><em>n</em><big>)</big><a class="headerlink" href="#io.BufferedReader.read1" title="Permalink to this definition">¶</a></dt> <dd><p>Read and return up to <em>n</em> bytes with only one call on the raw stream. If at least one byte is buffered, only buffered bytes are returned. Otherwise, one raw stream read call is made.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="io.BufferedWriter"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedWriter</tt><big>(</big><em>raw</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><big>)</big><a class="headerlink" href="#io.BufferedWriter" title="Permalink to this definition">¶</a></dt> <dd><p>A buffer providing higher-level access to a writeable, sequential <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> object. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>. When writing to this object, data is normally held into an internal buffer. The buffer will be written out to the underlying <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> object under various conditions, including:</p> <ul class="simple"> <li>when the buffer gets too small for all pending data;</li> <li>when <a class="reference internal" href="#io.BufferedWriter.flush" title="io.BufferedWriter.flush"><tt class="xref py py-meth docutils literal"><span class="pre">flush()</span></tt></a> is called;</li> <li>when a <tt class="xref py py-meth docutils literal"><span class="pre">seek()</span></tt> is requested (for <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> objects);</li> <li>when the <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> object is closed or destroyed.</li> </ul> <p>The constructor creates a <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> for the given writeable <em>raw</em> stream. If the <em>buffer_size</em> is not given, it defaults to <a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><tt class="xref py py-data docutils literal"><span class="pre">DEFAULT_BUFFER_SIZE</span></tt></a>.</p> <p>A third argument, <em>max_buffer_size</em>, is supported, but unused and deprecated.</p> <p><a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> provides or overrides these methods in addition to those from <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> and <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p> <dl class="method"> <dt id="io.BufferedWriter.flush"> <tt class="descname">flush</tt><big>(</big><big>)</big><a class="headerlink" href="#io.BufferedWriter.flush" title="Permalink to this definition">¶</a></dt> <dd><p>Force bytes held in the buffer into the raw stream. A <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> should be raised if the raw stream blocks.</p> </dd></dl> <dl class="method"> <dt id="io.BufferedWriter.write"> <tt class="descname">write</tt><big>(</big><em>b</em><big>)</big><a class="headerlink" href="#io.BufferedWriter.write" title="Permalink to this definition">¶</a></dt> <dd><p>Write the bytes or bytearray object, <em>b</em> and return the number of bytes written. When in non-blocking mode, a <a class="reference internal" href="#io.BlockingIOError" title="io.BlockingIOError"><tt class="xref py py-exc docutils literal"><span class="pre">BlockingIOError</span></tt></a> is raised if the buffer needs to be written out but the raw stream blocks.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="io.BufferedRandom"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedRandom</tt><big>(</big><em>raw</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><big>)</big><a class="headerlink" href="#io.BufferedRandom" title="Permalink to this definition">¶</a></dt> <dd><p>A buffered interface to random access streams. It inherits <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> and <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a>, and further supports <tt class="xref py py-meth docutils literal"><span class="pre">seek()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">tell()</span></tt> functionality.</p> <p>The constructor creates a reader and writer for a seekable raw stream, given in the first argument. If the <em>buffer_size</em> is omitted it defaults to <a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><tt class="xref py py-data docutils literal"><span class="pre">DEFAULT_BUFFER_SIZE</span></tt></a>.</p> <p>A third argument, <em>max_buffer_size</em>, is supported, but unused and deprecated.</p> <p><a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> is capable of anything <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a> or <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a> can do.</p> </dd></dl> <dl class="class"> <dt id="io.BufferedRWPair"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">BufferedRWPair</tt><big>(</big><em>reader</em>, <em>writer</em>, <em>buffer_size=DEFAULT_BUFFER_SIZE</em><big>)</big><a class="headerlink" href="#io.BufferedRWPair" title="Permalink to this definition">¶</a></dt> <dd><p>A buffered I/O object combining two unidirectional <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> objects – one readable, the other writeable – into a single bidirectional endpoint. It inherits <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>.</p> <p><em>reader</em> and <em>writer</em> are <a class="reference internal" href="#io.RawIOBase" title="io.RawIOBase"><tt class="xref py py-class docutils literal"><span class="pre">RawIOBase</span></tt></a> objects that are readable and writeable respectively. If the <em>buffer_size</em> is omitted it defaults to <a class="reference internal" href="#io.DEFAULT_BUFFER_SIZE" title="io.DEFAULT_BUFFER_SIZE"><tt class="xref py py-data docutils literal"><span class="pre">DEFAULT_BUFFER_SIZE</span></tt></a>.</p> <p>A fourth argument, <em>max_buffer_size</em>, is supported, but unused and deprecated.</p> <p><a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a> implements all of <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a>‘s methods except for <a class="reference internal" href="#io.BufferedIOBase.detach" title="io.BufferedIOBase.detach"><tt class="xref py py-meth docutils literal"><span class="pre">detach()</span></tt></a>, which raises <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><tt class="xref py py-exc docutils literal"><span class="pre">UnsupportedOperation</span></tt></a>.</p> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last"><a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a> does not attempt to synchronize accesses to its underlying raw streams. You should not pass it the same object as reader and writer; use <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> instead.</p> </div> </dd></dl> </div> <div class="section" id="text-i-o"> <h2>15.2.5. Text I/O<a class="headerlink" href="#text-i-o" title="Permalink to this headline">¶</a></h2> <dl class="class"> <dt id="io.TextIOBase"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">TextIOBase</tt><a class="headerlink" href="#io.TextIOBase" title="Permalink to this definition">¶</a></dt> <dd><p>Base class for text streams. This class provides an unicode character and line based interface to stream I/O. There is no <tt class="xref py py-meth docutils literal"><span class="pre">readinto()</span></tt> method because Python’s <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> strings are immutable. It inherits <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>. There is no public constructor.</p> <p><a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> provides or overrides these data attributes and methods in addition to those from <a class="reference internal" href="#io.IOBase" title="io.IOBase"><tt class="xref py py-class docutils literal"><span class="pre">IOBase</span></tt></a>:</p> <dl class="attribute"> <dt id="io.TextIOBase.encoding"> <tt class="descname">encoding</tt><a class="headerlink" href="#io.TextIOBase.encoding" title="Permalink to this definition">¶</a></dt> <dd><p>The name of the encoding used to decode the stream’s bytes into strings, and to encode strings into bytes.</p> </dd></dl> <dl class="attribute"> <dt id="io.TextIOBase.errors"> <tt class="descname">errors</tt><a class="headerlink" href="#io.TextIOBase.errors" title="Permalink to this definition">¶</a></dt> <dd><p>The error setting of the decoder or encoder.</p> </dd></dl> <dl class="attribute"> <dt id="io.TextIOBase.newlines"> <tt class="descname">newlines</tt><a class="headerlink" href="#io.TextIOBase.newlines" title="Permalink to this definition">¶</a></dt> <dd><p>A string, a tuple of strings, or <tt class="docutils literal"><span class="pre">None</span></tt>, indicating the newlines translated so far. Depending on the implementation and the initial constructor flags, this may not be available.</p> </dd></dl> <dl class="attribute"> <dt id="io.TextIOBase.buffer"> <tt class="descname">buffer</tt><a class="headerlink" href="#io.TextIOBase.buffer" title="Permalink to this definition">¶</a></dt> <dd><p>The underlying binary buffer (a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> instance) that <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> deals with. This is not part of the <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> API and may not exist on some implementations.</p> </dd></dl> <dl class="method"> <dt id="io.TextIOBase.detach"> <tt class="descname">detach</tt><big>(</big><big>)</big><a class="headerlink" href="#io.TextIOBase.detach" title="Permalink to this definition">¶</a></dt> <dd><p>Separate the underlying binary buffer from the <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> and return it.</p> <p>After the underlying buffer has been detached, the <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> is in an unusable state.</p> <p>Some <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> implementations, like <a class="reference internal" href="stringio.html#module-StringIO" title="StringIO: Read and write strings as if they were files."><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a>, may not have the concept of an underlying buffer and calling this method will raise <a class="reference internal" href="#io.UnsupportedOperation" title="io.UnsupportedOperation"><tt class="xref py py-exc docutils literal"><span class="pre">UnsupportedOperation</span></tt></a>.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.7.</span></p> </dd></dl> <dl class="method"> <dt id="io.TextIOBase.read"> <tt class="descname">read</tt><big>(</big><em>n</em><big>)</big><a class="headerlink" href="#io.TextIOBase.read" title="Permalink to this definition">¶</a></dt> <dd><p>Read and return at most <em>n</em> characters from the stream as a single <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a>. If <em>n</em> is negative or <tt class="docutils literal"><span class="pre">None</span></tt>, reads until EOF.</p> </dd></dl> <dl class="method"> <dt id="io.TextIOBase.readline"> <tt class="descname">readline</tt><big>(</big><em>limit=-1</em><big>)</big><a class="headerlink" href="#io.TextIOBase.readline" title="Permalink to this definition">¶</a></dt> <dd><p>Read until newline or EOF and return a single <tt class="docutils literal"><span class="pre">unicode</span></tt>. If the stream is already at EOF, an empty string is returned.</p> <p>If <em>limit</em> is specified, at most <em>limit</em> characters will be read.</p> </dd></dl> <dl class="method"> <dt id="io.TextIOBase.seek"> <tt class="descname">seek</tt><big>(</big><em>offset</em>, <em>whence=SEEK_SET</em><big>)</big><a class="headerlink" href="#io.TextIOBase.seek" title="Permalink to this definition">¶</a></dt> <dd><p>Change the stream position to the given <em>offset</em>. Behaviour depends on the <em>whence</em> parameter:</p> <ul class="simple"> <li><tt class="xref py py-data docutils literal"><span class="pre">SEEK_SET</span></tt> or <tt class="docutils literal"><span class="pre">0</span></tt>: seek from the start of the stream (the default); <em>offset</em> must either be a number returned by <a class="reference internal" href="#io.TextIOBase.tell" title="io.TextIOBase.tell"><tt class="xref py py-meth docutils literal"><span class="pre">TextIOBase.tell()</span></tt></a>, or zero. Any other <em>offset</em> value produces undefined behaviour.</li> <li><tt class="xref py py-data docutils literal"><span class="pre">SEEK_CUR</span></tt> or <tt class="docutils literal"><span class="pre">1</span></tt>: “seek” to the current position; <em>offset</em> must be zero, which is a no-operation (all other values are unsupported).</li> <li><tt class="xref py py-data docutils literal"><span class="pre">SEEK_END</span></tt> or <tt class="docutils literal"><span class="pre">2</span></tt>: seek to the end of the stream; <em>offset</em> must be zero (all other values are unsupported).</li> </ul> <p>Return the new absolute position as an opaque number.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.7: </span>The <tt class="docutils literal"><span class="pre">SEEK_*</span></tt> constants.</p> </dd></dl> <dl class="method"> <dt id="io.TextIOBase.tell"> <tt class="descname">tell</tt><big>(</big><big>)</big><a class="headerlink" href="#io.TextIOBase.tell" title="Permalink to this definition">¶</a></dt> <dd><p>Return the current stream position as an opaque number. The number does not usually represent a number of bytes in the underlying binary storage.</p> </dd></dl> <dl class="method"> <dt id="io.TextIOBase.write"> <tt class="descname">write</tt><big>(</big><em>s</em><big>)</big><a class="headerlink" href="#io.TextIOBase.write" title="Permalink to this definition">¶</a></dt> <dd><p>Write the <a class="reference internal" href="functions.html#unicode" title="unicode"><tt class="xref py py-class docutils literal"><span class="pre">unicode</span></tt></a> string <em>s</em> to the stream and return the number of characters written.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="io.TextIOWrapper"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">TextIOWrapper</tt><big>(</big><em>buffer</em>, <em>encoding=None</em>, <em>errors=None</em>, <em>newline=None</em>, <em>line_buffering=False</em><big>)</big><a class="headerlink" href="#io.TextIOWrapper" title="Permalink to this definition">¶</a></dt> <dd><p>A buffered text stream over a <a class="reference internal" href="#io.BufferedIOBase" title="io.BufferedIOBase"><tt class="xref py py-class docutils literal"><span class="pre">BufferedIOBase</span></tt></a> binary stream. It inherits <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a>.</p> <p><em>encoding</em> gives the name of the encoding that the stream will be decoded or encoded with. It defaults to <a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><tt class="xref py py-func docutils literal"><span class="pre">locale.getpreferredencoding()</span></tt></a>.</p> <p><em>errors</em> is an optional string that specifies how encoding and decoding errors are to be handled. Pass <tt class="docutils literal"><span class="pre">'strict'</span></tt> to raise a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> exception if there is an encoding error (the default of <tt class="docutils literal"><span class="pre">None</span></tt> has the same effect), or pass <tt class="docutils literal"><span class="pre">'ignore'</span></tt> to ignore errors. (Note that ignoring encoding errors can lead to data loss.) <tt class="docutils literal"><span class="pre">'replace'</span></tt> causes a replacement marker (such as <tt class="docutils literal"><span class="pre">'?'</span></tt>) to be inserted where there is malformed data. When writing, <tt class="docutils literal"><span class="pre">'xmlcharrefreplace'</span></tt> (replace with the appropriate XML character reference) or <tt class="docutils literal"><span class="pre">'backslashreplace'</span></tt> (replace with backslashed escape sequences) can be used. Any other error handling name that has been registered with <a class="reference internal" href="codecs.html#codecs.register_error" title="codecs.register_error"><tt class="xref py py-func docutils literal"><span class="pre">codecs.register_error()</span></tt></a> is also valid.</p> <p id="index-1"><em>newline</em> controls how line endings are handled. It can be <tt class="docutils literal"><span class="pre">None</span></tt>, <tt class="docutils literal"><span class="pre">''</span></tt>, <tt class="docutils literal"><span class="pre">'\n'</span></tt>, <tt class="docutils literal"><span class="pre">'\r'</span></tt>, and <tt class="docutils literal"><span class="pre">'\r\n'</span></tt>. It works as follows:</p> <ul class="simple"> <li>On input, if <em>newline</em> is <tt class="docutils literal"><span class="pre">None</span></tt>, <a class="reference internal" href="../glossary.html#term-universal-newlines"><em class="xref std std-term">universal newlines</em></a> mode is enabled. Lines in the input can end in <tt class="docutils literal"><span class="pre">'\n'</span></tt>, <tt class="docutils literal"><span class="pre">'\r'</span></tt>, or <tt class="docutils literal"><span class="pre">'\r\n'</span></tt>, and these are translated into <tt class="docutils literal"><span class="pre">'\n'</span></tt> before being returned to the caller. If it is <tt class="docutils literal"><span class="pre">''</span></tt>, universal newlines mode is enabled, but line endings are returned to the caller untranslated. If it has any of the other legal values, input lines are only terminated by the given string, and the line ending is returned to the caller untranslated.</li> <li>On output, if <em>newline</em> is <tt class="docutils literal"><span class="pre">None</span></tt>, any <tt class="docutils literal"><span class="pre">'\n'</span></tt> characters written are translated to the system default line separator, <a class="reference internal" href="os.html#os.linesep" title="os.linesep"><tt class="xref py py-data docutils literal"><span class="pre">os.linesep</span></tt></a>. If <em>newline</em> is <tt class="docutils literal"><span class="pre">''</span></tt>, no translation takes place. If <em>newline</em> is any of the other legal values, any <tt class="docutils literal"><span class="pre">'\n'</span></tt> characters written are translated to the given string.</li> </ul> <p>If <em>line_buffering</em> is <tt class="docutils literal"><span class="pre">True</span></tt>, <tt class="xref py py-meth docutils literal"><span class="pre">flush()</span></tt> is implied when a call to write contains a newline character.</p> <p><a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a> provides one attribute in addition to those of <a class="reference internal" href="#io.TextIOBase" title="io.TextIOBase"><tt class="xref py py-class docutils literal"><span class="pre">TextIOBase</span></tt></a> and its parents:</p> <dl class="attribute"> <dt id="io.TextIOWrapper.line_buffering"> <tt class="descname">line_buffering</tt><a class="headerlink" href="#io.TextIOWrapper.line_buffering" title="Permalink to this definition">¶</a></dt> <dd><p>Whether line buffering is enabled.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="io.StringIO"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">StringIO</tt><big>(</big><em>initial_value=u''</em>, <em>newline=None</em><big>)</big><a class="headerlink" href="#io.StringIO" title="Permalink to this definition">¶</a></dt> <dd><p>An in-memory stream for unicode text. It inherits <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a>.</p> <p>The initial value of the buffer (an empty unicode string by default) can be set by providing <em>initial_value</em>. The <em>newline</em> argument works like that of <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a>. The default is to do no newline translation.</p> <p><a class="reference internal" href="stringio.html#module-StringIO" title="StringIO: Read and write strings as if they were files."><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> provides this method in addition to those from <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a> and its parents:</p> <dl class="method"> <dt id="io.StringIO.getvalue"> <tt class="descname">getvalue</tt><big>(</big><big>)</big><a class="headerlink" href="#io.StringIO.getvalue" title="Permalink to this definition">¶</a></dt> <dd><p>Return a <tt class="docutils literal"><span class="pre">unicode</span></tt> containing the entire contents of the buffer at any time before the <a class="reference internal" href="stringio.html#module-StringIO" title="StringIO: Read and write strings as if they were files."><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a> object’s <tt class="xref py py-meth docutils literal"><span class="pre">close()</span></tt> method is called.</p> </dd></dl> <p>Example usage:</p> <div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">io</span> <span class="n">output</span> <span class="o">=</span> <span class="n">io</span><span class="o">.</span><span class="n">StringIO</span><span class="p">()</span> <span class="n">output</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">u'First line.</span><span class="se">\n</span><span class="s">'</span><span class="p">)</span> <span class="n">output</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="s">u'Second line.</span><span class="se">\n</span><span class="s">'</span><span class="p">)</span> <span class="c"># Retrieve file contents -- this will be</span> <span class="c"># u'First line.\nSecond line.\n'</span> <span class="n">contents</span> <span class="o">=</span> <span class="n">output</span><span class="o">.</span><span class="n">getvalue</span><span class="p">()</span> <span class="c"># Close object and discard memory buffer --</span> <span class="c"># .getvalue() will now raise an exception.</span> <span class="n">output</span><span class="o">.</span><span class="n">close</span><span class="p">()</span> </pre></div> </div> </dd></dl> <span class="target" id="index-2"></span><dl class="class"> <dt id="io.IncrementalNewlineDecoder"> <em class="property">class </em><tt class="descclassname">io.</tt><tt class="descname">IncrementalNewlineDecoder</tt><a class="headerlink" href="#io.IncrementalNewlineDecoder" title="Permalink to this definition">¶</a></dt> <dd><p>A helper codec that decodes newlines for <a class="reference internal" href="../glossary.html#term-universal-newlines"><em class="xref std std-term">universal newlines</em></a> mode. It inherits <a class="reference internal" href="codecs.html#codecs.IncrementalDecoder" title="codecs.IncrementalDecoder"><tt class="xref py py-class docutils literal"><span class="pre">codecs.IncrementalDecoder</span></tt></a>.</p> </dd></dl> </div> <div class="section" id="advanced-topics"> <h2>15.2.6. Advanced topics<a class="headerlink" href="#advanced-topics" title="Permalink to this headline">¶</a></h2> <p>Here we will discuss several advanced topics pertaining to the concrete I/O implementations described above.</p> <div class="section" id="performance"> <h3>15.2.6.1. Performance<a class="headerlink" href="#performance" title="Permalink to this headline">¶</a></h3> <div class="section" id="binary-i-o"> <h4>15.2.6.1.1. Binary I/O<a class="headerlink" href="#binary-i-o" title="Permalink to this headline">¶</a></h4> <p>By reading and writing only large chunks of data even when the user asks for a single byte, buffered I/O is designed to hide any inefficiency in calling and executing the operating system’s unbuffered I/O routines. The gain will vary very much depending on the OS and the kind of I/O which is performed (for example, on some contemporary OSes such as Linux, unbuffered disk I/O can be as fast as buffered I/O). The bottom line, however, is that buffered I/O will offer you predictable performance regardless of the platform and the backing device. Therefore, it is most always preferable to use buffered I/O rather than unbuffered I/O.</p> </div> <div class="section" id="id1"> <h4>15.2.6.1.2. Text I/O<a class="headerlink" href="#id1" title="Permalink to this headline">¶</a></h4> <p>Text I/O over a binary storage (such as a file) is significantly slower than binary I/O over the same storage, because it implies conversions from unicode to binary data using a character codec. This can become noticeable if you handle huge amounts of text data (for example very large log files). Also, <tt class="xref py py-meth docutils literal"><span class="pre">TextIOWrapper.tell()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">TextIOWrapper.seek()</span></tt> are both quite slow due to the reconstruction algorithm used.</p> <p><a class="reference internal" href="stringio.html#module-StringIO" title="StringIO: Read and write strings as if they were files."><tt class="xref py py-class docutils literal"><span class="pre">StringIO</span></tt></a>, however, is a native in-memory unicode container and will exhibit similar speed to <a class="reference internal" href="#io.BytesIO" title="io.BytesIO"><tt class="xref py py-class docutils literal"><span class="pre">BytesIO</span></tt></a>.</p> </div> </div> <div class="section" id="multi-threading"> <h3>15.2.6.2. Multi-threading<a class="headerlink" href="#multi-threading" title="Permalink to this headline">¶</a></h3> <p><a class="reference internal" href="#io.FileIO" title="io.FileIO"><tt class="xref py py-class docutils literal"><span class="pre">FileIO</span></tt></a> objects are thread-safe to the extent that the operating system calls (such as <tt class="docutils literal"><span class="pre">read(2)</span></tt> under Unix) they are wrapping are thread-safe too.</p> <p>Binary buffered objects (instances of <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a>, <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a>, <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a>) protect their internal structures using a lock; it is therefore safe to call them from multiple threads at once.</p> <p><a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a> objects are not thread-safe.</p> </div> <div class="section" id="reentrancy"> <h3>15.2.6.3. Reentrancy<a class="headerlink" href="#reentrancy" title="Permalink to this headline">¶</a></h3> <p>Binary buffered objects (instances of <a class="reference internal" href="#io.BufferedReader" title="io.BufferedReader"><tt class="xref py py-class docutils literal"><span class="pre">BufferedReader</span></tt></a>, <a class="reference internal" href="#io.BufferedWriter" title="io.BufferedWriter"><tt class="xref py py-class docutils literal"><span class="pre">BufferedWriter</span></tt></a>, <a class="reference internal" href="#io.BufferedRandom" title="io.BufferedRandom"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRandom</span></tt></a> and <a class="reference internal" href="#io.BufferedRWPair" title="io.BufferedRWPair"><tt class="xref py py-class docutils literal"><span class="pre">BufferedRWPair</span></tt></a>) are not reentrant. While reentrant calls will not happen in normal situations, they can arise if you are doing I/O in a <a class="reference internal" href="signal.html#module-signal" title="signal: Set handlers for asynchronous events."><tt class="xref py py-mod docutils literal"><span class="pre">signal</span></tt></a> handler. If it is attempted to enter a buffered object again while already being accessed <em>from the same thread</em>, then a <a class="reference internal" href="exceptions.html#exceptions.RuntimeError" title="exceptions.RuntimeError"><tt class="xref py py-exc docutils literal"><span class="pre">RuntimeError</span></tt></a> is raised.</p> <p>The above implicitly extends to text files, since the <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> function will wrap a buffered object inside a <a class="reference internal" href="#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">TextIOWrapper</span></tt></a>. This includes standard streams and therefore affects the built-in function <a class="reference internal" href="functions.html#print" title="print"><tt class="xref py py-func docutils literal"><span class="pre">print()</span></tt></a> as well.</p> </div> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">15.2. <tt class="docutils literal"><span class="pre">io</span></tt> — Core tools for working with streams</a><ul> <li><a class="reference internal" href="#module-interface">15.2.1. Module Interface</a></li> <li><a class="reference internal" href="#i-o-base-classes">15.2.2. I/O Base Classes</a></li> <li><a class="reference internal" href="#raw-file-i-o">15.2.3. Raw File I/O</a></li> <li><a class="reference internal" href="#buffered-streams">15.2.4. Buffered Streams</a></li> <li><a class="reference internal" href="#text-i-o">15.2.5. Text I/O</a></li> <li><a class="reference internal" href="#advanced-topics">15.2.6. Advanced topics</a><ul> <li><a class="reference internal" href="#performance">15.2.6.1. Performance</a><ul> <li><a class="reference internal" href="#binary-i-o">15.2.6.1.1. Binary I/O</a></li> <li><a class="reference internal" href="#id1">15.2.6.1.2. Text I/O</a></li> </ul> </li> <li><a class="reference internal" href="#multi-threading">15.2.6.2. Multi-threading</a></li> <li><a class="reference internal" href="#reentrancy">15.2.6.3. Reentrancy</a></li> </ul> </li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="os.html" title="previous chapter">15.1. <tt class="docutils literal"><span class="pre">os</span></tt> — Miscellaneous operating system interfaces</a></p> <h4>Next topic</h4> <p class="topless"><a href="time.html" title="next chapter">15.3. <tt class="docutils literal"><span class="pre">time</span></tt> — Time access and conversions</a></p> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li><a href="../_sources/library/io.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <form class="search" action="../search.html" method="get"> <input type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="time.html" title="15.3. time — Time access and conversions" >next</a> |</li> <li class="right" > <a href="os.html" title="15.1. os — Miscellaneous operating system interfaces" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="http://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.5 documentation</a> » </li> <li><a href="index.html" >The Python Standard Library</a> »</li> <li><a href="allos.html" >15. Generic Operating System Services</a> »</li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 1990-2019, Python Software Foundation. <br /> The Python Software Foundation is a non-profit corporation. <a href="http://www.python.org/psf/donations/">Please donate.</a> <br /> Last updated on Jul 03, 2019. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.1.3. </div> </body> </html>
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