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<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <title>21.6. chunk — Read IFF chunked data — Python 2.7.18 documentation</title> <link rel="stylesheet" type="text/css" href="../_static/pygments.css" /> <link rel="stylesheet" type="text/css" href="../_static/classic.css" /> <script data-url_root="../" id="documentation_options" src="../_static/documentation_options.js"></script> <script src="../_static/jquery.js"></script> <script src="../_static/underscore.js"></script> <script src="../_static/doctools.js"></script> <script src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.18 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="21.7. colorsys — Conversions between color systems" href="colorsys.html" /> <link rel="prev" title="21.5. wave — Read and write WAV files" href="wave.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/library/chunk.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"> This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>. You should install the python3 and python3-doc packages and read the <a href="file:///usr/share/doc/python3-doc/html/library/chunk.html"> Python documentation for the Python3 version packaged in this release</a>. </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" 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="21.7. colorsys — Conversions between color systems" accesskey="N">next</a> |</li> <li class="right" > <a href="wave.html" title="21.5. 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> <a href="../index.html">Python 2.7.18 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"><span class="section-number">21. </span>Multimedia Services</a> »</li> <li class="nav-item nav-item-this"><a href=""><span class="section-number">21.6. </span><code class="xref py py-mod docutils literal notranslate"><span class="pre">chunk</span></code> — Read IFF chunked data</a></li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <section id="module-chunk"> <span id="chunk-read-iff-chunked-data"></span><h1><span class="section-number">21.6. </span><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 id="index-0">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-default"> <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 <code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code> exception.</p> <dl class="py class"> <dt class="sig sig-object py" id="chunk.Chunk"> <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">chunk.</span></span><span class="sig-name descname"><span class="pre">Chunk</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">file</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">align</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">bigendian</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">inclheader</span></span></em><span class="optional">]</span><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 <a class="reference internal" href="stdtypes.html#file.read" title="file.read"><code class="xref py py-meth docutils literal notranslate"><span class="pre">read()</span></code></a>. If the methods <a class="reference internal" href="stdtypes.html#file.seek" title="file.seek"><code class="xref py py-meth docutils literal notranslate"><span class="pre">seek()</span></code></a> and <a class="reference internal" href="stdtypes.html#file.tell" title="file.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="py method"> <dt class="sig sig-object py" id="chunk.Chunk.getname"> <span class="sig-name descname"><span class="pre">getname</span></span><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="py method"> <dt class="sig sig-object py" id="chunk.Chunk.getsize"> <span class="sig-name descname"><span class="pre">getsize</span></span><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="py method"> <dt class="sig sig-object py" id="chunk.Chunk.close"> <span class="sig-name descname"><span class="pre">close</span></span><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 <code class="xref py py-exc docutils literal notranslate"><span class="pre">IOError</span></code> 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.</p> <dl class="py method"> <dt class="sig sig-object py" id="chunk.Chunk.isatty"> <span class="sig-name descname"><span class="pre">isatty</span></span><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="py method"> <dt class="sig sig-object py" id="chunk.Chunk.seek"> <span class="sig-name descname"><span class="pre">seek</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">pos</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">whence</span></span></em><span class="optional">]</span><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="py method"> <dt class="sig sig-object py" id="chunk.Chunk.tell"> <span class="sig-name descname"><span class="pre">tell</span></span><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="py method"> <dt class="sig sig-object py" id="chunk.Chunk.read"> <span class="sig-name descname"><span class="pre">read</span></span><span class="sig-paren">(</span><span class="optional">[</span><em class="sig-param"><span class="n"><span class="pre">size</span></span></em><span class="optional">]</span><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. The bytes are returned as a string object. An empty string is returned when the end of the chunk is encountered immediately.</p> </dd></dl> <dl class="py method"> <dt class="sig sig-object py" id="chunk.Chunk.skip"> <span class="sig-name descname"><span class="pre">skip</span></span><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">''</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> </section> <div class="clearer"></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"><span class="section-number">21.5. </span><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"><span class="section-number">21.7. </span><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="../_sources/library/chunk.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3 id="searchlabel">Quick search</h3> <div class="searchformwrapper"> <form class="search" action="../search.html" method="get"> <input type="text" name="q" aria-labelledby="searchlabel" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"/> <input type="submit" value="Go" /> </form> </div> </div> <script>$('#searchbox').show(0);</script> </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="21.7. colorsys — Conversions between color systems" >next</a> |</li> <li class="right" > <a href="wave.html" title="21.5. 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> <a href="../index.html">Python 2.7.18 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" ><span class="section-number">21. </span>Multimedia Services</a> »</li> <li class="nav-item nav-item-this"><a href=""><span class="section-number">21.6. </span><code class="xref py py-mod docutils literal notranslate"><span class="pre">chunk</span></code> — Read IFF chunked data</a></li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 1990-2024, 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 November 21, 2024. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 4.3.2. </div> </body> </html>