<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8" /> <title>chunk — Read IFF chunked data — Python 3.7.4 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></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/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.7.4 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="colorsys — Conversions between color systems" href="colorsys.html" /> <link rel="prev" title="wave — Read and write WAV files" href="wave.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/library/chunk.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> <script type="text/javascript" src="../_static/switchers.js"></script> <style> @media only screen { table.full-width-table { width: 100%; } } </style> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="colorsys.html" title="colorsys — Conversions between color systems" accesskey="N">next</a> |</li> <li class="right" > <a href="wave.html" title="wave — Read and write WAV files" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <span class="language_switcher_placeholder">en</span> <span class="version_switcher_placeholder">3.7.4</span> <a href="../index.html">Documentation </a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="mm.html" accesskey="U">Multimedia Services</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" 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> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-chunk"> <span id="chunk-read-iff-chunked-data"></span><h1><a class="reference internal" href="#module-chunk" title="chunk: Module to read IFF chunks."><code class="xref py py-mod docutils literal notranslate"><span class="pre">chunk</span></code></a> — Read IFF chunked data<a class="headerlink" href="#module-chunk" title="Permalink to this headline">¶</a></h1> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/chunk.py">Lib/chunk.py</a></p> <hr class="docutils" id="index-0" /> <p>This module provides an interface for reading files that use EA IFF 85 chunks. <a class="footnote-reference brackets" href="#id2" id="id1">1</a> This format is used in at least the Audio Interchange File Format (AIFF/AIFF-C) and the Real Media File Format (RMFF). The WAVE audio file format is closely related and can also be read using this module.</p> <p>A chunk has the following structure:</p> <table class="docutils align-center"> <colgroup> <col style="width: 19%" /> <col style="width: 17%" /> <col style="width: 65%" /> </colgroup> <thead> <tr class="row-odd"><th class="head"><p>Offset</p></th> <th class="head"><p>Length</p></th> <th class="head"><p>Contents</p></th> </tr> </thead> <tbody> <tr class="row-even"><td><p>0</p></td> <td><p>4</p></td> <td><p>Chunk ID</p></td> </tr> <tr class="row-odd"><td><p>4</p></td> <td><p>4</p></td> <td><p>Size of chunk in big-endian byte order, not including the header</p></td> </tr> <tr class="row-even"><td><p>8</p></td> <td><p><em>n</em></p></td> <td><p>Data bytes, where <em>n</em> is the size given in the preceding field</p></td> </tr> <tr class="row-odd"><td><p>8 + <em>n</em></p></td> <td><p>0 or 1</p></td> <td><p>Pad byte needed if <em>n</em> is odd and chunk alignment is used</p></td> </tr> </tbody> </table> <p>The ID is a 4-byte string which identifies the type of chunk.</p> <p>The size field (a 32-bit value, encoded using big-endian byte order) gives the size of the chunk data, not including the 8-byte header.</p> <p>Usually an IFF-type file consists of one or more chunks. The proposed usage of the <a class="reference internal" href="#chunk.Chunk" title="chunk.Chunk"><code class="xref py py-class docutils literal notranslate"><span class="pre">Chunk</span></code></a> class defined here is to instantiate an instance at the start of each chunk and read from the instance until it reaches the end, after which a new instance can be instantiated. At the end of the file, creating a new instance will fail with an <a class="reference internal" href="exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a> exception.</p> <dl class="class"> <dt id="chunk.Chunk"> <em class="property">class </em><code class="descclassname">chunk.</code><code class="descname">Chunk</code><span class="sig-paren">(</span><em>file</em>, <em>align=True</em>, <em>bigendian=True</em>, <em>inclheader=False</em><span class="sig-paren">)</span><a class="headerlink" href="#chunk.Chunk" title="Permalink to this definition">¶</a></dt> <dd><p>Class which represents a chunk. The <em>file</em> argument is expected to be a file-like object. An instance of this class is specifically allowed. The only method that is needed is <code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code>. If the methods <a class="reference internal" href="io.html#io.IOBase.seek" title="io.IOBase.seek"><code class="xref py py-meth docutils literal notranslate"><span class="pre">seek()</span></code></a> and <a class="reference internal" href="io.html#io.IOBase.tell" title="io.IOBase.tell"><code class="xref py py-meth docutils literal notranslate"><span class="pre">tell()</span></code></a> are present and don’t raise an exception, they are also used. If these methods are present and raise an exception, they are expected to not have altered the object. If the optional argument <em>align</em> is true, chunks are assumed to be aligned on 2-byte boundaries. If <em>align</em> is false, no alignment is assumed. The default value is true. If the optional argument <em>bigendian</em> is false, the chunk size is assumed to be in little-endian order. This is needed for WAVE audio files. The default value is true. If the optional argument <em>inclheader</em> is true, the size given in the chunk header includes the size of the header. The default value is false.</p> <p>A <a class="reference internal" href="#chunk.Chunk" title="chunk.Chunk"><code class="xref py py-class docutils literal notranslate"><span class="pre">Chunk</span></code></a> object supports the following methods:</p> <dl class="method"> <dt id="chunk.Chunk.getname"> <code class="descname">getname</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#chunk.Chunk.getname" title="Permalink to this definition">¶</a></dt> <dd><p>Returns the name (ID) of the chunk. This is the first 4 bytes of the chunk.</p> </dd></dl> <dl class="method"> <dt id="chunk.Chunk.getsize"> <code class="descname">getsize</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#chunk.Chunk.getsize" title="Permalink to this definition">¶</a></dt> <dd><p>Returns the size of the chunk.</p> </dd></dl> <dl class="method"> <dt id="chunk.Chunk.close"> <code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#chunk.Chunk.close" title="Permalink to this definition">¶</a></dt> <dd><p>Close and skip to the end of the chunk. This does not close the underlying file.</p> </dd></dl> <p>The remaining methods will raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a> if called after the <a class="reference internal" href="#chunk.Chunk.close" title="chunk.Chunk.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> method has been called. Before Python 3.3, they used to raise <a class="reference internal" href="exceptions.html#IOError" title="IOError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IOError</span></code></a>, now an alias of <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">OSError</span></code></a>.</p> <dl class="method"> <dt id="chunk.Chunk.isatty"> <code class="descname">isatty</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#chunk.Chunk.isatty" title="Permalink to this definition">¶</a></dt> <dd><p>Returns <code class="docutils literal notranslate"><span class="pre">False</span></code>.</p> </dd></dl> <dl class="method"> <dt id="chunk.Chunk.seek"> <code class="descname">seek</code><span class="sig-paren">(</span><em>pos</em>, <em>whence=0</em><span class="sig-paren">)</span><a class="headerlink" href="#chunk.Chunk.seek" title="Permalink to this definition">¶</a></dt> <dd><p>Set the chunk’s current position. The <em>whence</em> argument is optional and defaults to <code class="docutils literal notranslate"><span class="pre">0</span></code> (absolute file positioning); other values are <code class="docutils literal notranslate"><span class="pre">1</span></code> (seek relative to the current position) and <code class="docutils literal notranslate"><span class="pre">2</span></code> (seek relative to the file’s end). There is no return value. If the underlying file does not allow seek, only forward seeks are allowed.</p> </dd></dl> <dl class="method"> <dt id="chunk.Chunk.tell"> <code class="descname">tell</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#chunk.Chunk.tell" title="Permalink to this definition">¶</a></dt> <dd><p>Return the current position into the chunk.</p> </dd></dl> <dl class="method"> <dt id="chunk.Chunk.read"> <code class="descname">read</code><span class="sig-paren">(</span><em>size=-1</em><span class="sig-paren">)</span><a class="headerlink" href="#chunk.Chunk.read" title="Permalink to this definition">¶</a></dt> <dd><p>Read at most <em>size</em> bytes from the chunk (less if the read hits the end of the chunk before obtaining <em>size</em> bytes). If the <em>size</em> argument is negative or omitted, read all data until the end of the chunk. An empty bytes object is returned when the end of the chunk is encountered immediately.</p> </dd></dl> <dl class="method"> <dt id="chunk.Chunk.skip"> <code class="descname">skip</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#chunk.Chunk.skip" title="Permalink to this definition">¶</a></dt> <dd><p>Skip to the end of the chunk. All further calls to <a class="reference internal" href="#chunk.Chunk.read" title="chunk.Chunk.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a> for the chunk will return <code class="docutils literal notranslate"><span class="pre">b''</span></code>. If you are not interested in the contents of the chunk, this method should be called so that the file points to the start of the next chunk.</p> </dd></dl> </dd></dl> <p class="rubric">Footnotes</p> <dl class="footnote brackets"> <dt class="label" id="id2"><span class="brackets"><a class="fn-backref" href="#id1">1</a></span></dt> <dd><p>“EA IFF 85” Standard for Interchange Format Files, Jerry Morrison, Electronic Arts, January 1985.</p> </dd> </dl> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h4>Previous topic</h4> <p class="topless"><a href="wave.html" title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">wave</span></code> — Read and write WAV files</a></p> <h4>Next topic</h4> <p class="topless"><a href="colorsys.html" title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">colorsys</span></code> — Conversions between color systems</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.7/Doc/library/chunk.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <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="colorsys.html" title="colorsys — Conversions between color systems" >next</a> |</li> <li class="right" > <a href="wave.html" title="wave — Read and write WAV files" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <span class="language_switcher_placeholder">en</span> <span class="version_switcher_placeholder">3.7.4</span> <a href="../index.html">Documentation </a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="mm.html" >Multimedia Services</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" 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> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 2001-2019, Python Software Foundation. <br /> The Python Software Foundation is a non-profit corporation. <a href="https://www.python.org/psf/donations/">Please donate.</a> <br /> Last updated on Jul 13, 2019. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 2.0.1. </div> </body> </html>