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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="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Data marshalling support — Python 3.6.7 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/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.6.7 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="Parsing arguments and building values" href="arg.html" /> <link rel="prev" title="Importing Modules" href="import.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/c-api/marshal.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </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="arg.html" title="Parsing arguments and building values" accesskey="N">next</a> |</li> <li class="right" > <a href="import.html" title="Importing Modules" 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">3.6.7 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >Python/C API Reference Manual</a> »</li> <li class="nav-item nav-item-2"><a href="utilities.html" accesskey="U">Utilities</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="data-marshalling-support"> <span id="marshalling-utils"></span><h1>Data marshalling support<a class="headerlink" href="#data-marshalling-support" title="Permalink to this headline">¶</a></h1> <p>These routines allow C code to work with serialized objects using the same data format as the <a class="reference internal" href="../library/marshal.html#module-marshal" title="marshal: Convert Python objects to streams of bytes and back (with different constraints)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">marshal</span></code></a> module. There are functions to write data into the serialization format, and additional functions that can be used to read the data back. Files used to store marshalled data must be opened in binary mode.</p> <p>Numeric values are stored with the least significant byte first.</p> <p>The module supports two versions of the data format: version 0 is the historical version, version 1 shares interned strings in the file, and upon unmarshalling. Version 2 uses a binary format for floating point numbers. <em>Py_MARSHAL_VERSION</em> indicates the current file format (currently 2).</p> <dl class="function"> <dt id="c.PyMarshal_WriteLongToFile"> void <code class="descname">PyMarshal_WriteLongToFile</code><span class="sig-paren">(</span>long<em> value</em>, FILE<em> *file</em>, int<em> version</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_WriteLongToFile" title="Permalink to this definition">¶</a></dt> <dd><p>Marshal a <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code> integer, <em>value</em>, to <em>file</em>. This will only write the least-significant 32 bits of <em>value</em>; regardless of the size of the native <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code> type. <em>version</em> indicates the file format.</p> </dd></dl> <dl class="function"> <dt id="c.PyMarshal_WriteObjectToFile"> void <code class="descname">PyMarshal_WriteObjectToFile</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *value</em>, FILE<em> *file</em>, int<em> version</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_WriteObjectToFile" title="Permalink to this definition">¶</a></dt> <dd><p>Marshal a Python object, <em>value</em>, to <em>file</em>. <em>version</em> indicates the file format.</p> </dd></dl> <dl class="function"> <dt id="c.PyMarshal_WriteObjectToString"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyMarshal_WriteObjectToString</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *value</em>, int<em> version</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_WriteObjectToString" title="Permalink to this definition">¶</a></dt> <dd><em class="refcount">Return value: New reference.</em><p>Return a bytes object containing the marshalled representation of <em>value</em>. <em>version</em> indicates the file format.</p> </dd></dl> <p>The following functions allow marshalled values to be read back in.</p> <dl class="function"> <dt id="c.PyMarshal_ReadLongFromFile"> long <code class="descname">PyMarshal_ReadLongFromFile</code><span class="sig-paren">(</span>FILE<em> *file</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadLongFromFile" title="Permalink to this definition">¶</a></dt> <dd><p>Return a C <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code> from the data stream in a <code class="xref c c-type docutils literal notranslate"><span class="pre">FILE*</span></code> opened for reading. Only a 32-bit value can be read in using this function, regardless of the native size of <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code>.</p> <p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>) and returns <code class="docutils literal notranslate"><span class="pre">-1</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.PyMarshal_ReadShortFromFile"> int <code class="descname">PyMarshal_ReadShortFromFile</code><span class="sig-paren">(</span>FILE<em> *file</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadShortFromFile" title="Permalink to this definition">¶</a></dt> <dd><p>Return a C <code class="xref c c-type docutils literal notranslate"><span class="pre">short</span></code> from the data stream in a <code class="xref c c-type docutils literal notranslate"><span class="pre">FILE*</span></code> opened for reading. Only a 16-bit value can be read in using this function, regardless of the native size of <code class="xref c c-type docutils literal notranslate"><span class="pre">short</span></code>.</p> <p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>) and returns <code class="docutils literal notranslate"><span class="pre">-1</span></code>.</p> </dd></dl> <dl class="function"> <dt id="c.PyMarshal_ReadObjectFromFile"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyMarshal_ReadObjectFromFile</code><span class="sig-paren">(</span>FILE<em> *file</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadObjectFromFile" title="Permalink to this definition">¶</a></dt> <dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a <code class="xref c c-type docutils literal notranslate"><span class="pre">FILE*</span></code> opened for reading.</p> <p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>, <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> or <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>) and returns <em>NULL</em>.</p> </dd></dl> <dl class="function"> <dt id="c.PyMarshal_ReadLastObjectFromFile"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyMarshal_ReadLastObjectFromFile</code><span class="sig-paren">(</span>FILE<em> *file</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadLastObjectFromFile" title="Permalink to this definition">¶</a></dt> <dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a <code class="xref c c-type docutils literal notranslate"><span class="pre">FILE*</span></code> opened for reading. Unlike <a class="reference internal" href="#c.PyMarshal_ReadObjectFromFile" title="PyMarshal_ReadObjectFromFile"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMarshal_ReadObjectFromFile()</span></code></a>, this function assumes that no further objects will be read from the file, allowing it to aggressively load file data into memory so that the de-serialization can operate from data in memory rather than reading a byte at a time from the file. Only use these variant if you are certain that you won’t be reading anything else from the file.</p> <p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>, <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> or <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>) and returns <em>NULL</em>.</p> </dd></dl> <dl class="function"> <dt id="c.PyMarshal_ReadObjectFromString"> <a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="descname">PyMarshal_ReadObjectFromString</code><span class="sig-paren">(</span>const char<em> *data</em>, Py_ssize_t<em> len</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadObjectFromString" title="Permalink to this definition">¶</a></dt> <dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a byte buffer containing <em>len</em> bytes pointed to by <em>data</em>.</p> <p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>, <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> or <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>) and returns <em>NULL</em>.</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="import.html" title="previous chapter">Importing Modules</a></p> <h4>Next topic</h4> <p class="topless"><a href="arg.html" title="next chapter">Parsing arguments and building values</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/3.6/Doc/c-api/marshal.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="arg.html" title="Parsing arguments and building values" >next</a> |</li> <li class="right" > <a href="import.html" title="Importing Modules" >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">3.6.7 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >Python/C API Reference Manual</a> »</li> <li class="nav-item nav-item-2"><a href="utilities.html" >Utilities</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> 2001-2021, 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 Aug 25, 2021. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.7.6. </div> </body> </html>