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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>11.5. marshal — Internal Python object serialization — Python 2.7.18 documentation</title> <link rel="stylesheet" href="../_static/classic.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 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="11.6. anydbm — Generic access to DBM-style databases" href="anydbm.html" /> <link rel="prev" title="11.4. shelve — Python object persistence" href="shelve.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/library/marshal.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div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"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/marshal.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="anydbm.html" title="11.6. anydbm — Generic access to DBM-style databases" accesskey="N">next</a> |</li> <li class="right" > <a href="shelve.html" title="11.4. shelve — Python object persistence" 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="persistence.html" accesskey="U">11. Data Persistence</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-marshal"> <span id="marshal-internal-python-object-serialization"></span><h1>11.5. <a class="reference internal" href="#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> — Internal Python object serialization<a class="headerlink" href="#module-marshal" title="Permalink to this headline">¶</a></h1> <p>This module contains functions that can read and write Python values in a binary format. The format is specific to Python, but independent of machine architecture issues (e.g., you can write a Python value to a file on a PC, transport the file to a Sun, and read it back there). Details of the format are undocumented on purpose; it may change between Python versions (although it rarely does). <a class="footnote-reference" href="#id2" id="id1">[1]</a></p> <p id="index-0">This is not a general “persistence” module. For general persistence and transfer of Python objects through RPC calls, see the modules <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> and <a class="reference internal" href="shelve.html#module-shelve" title="shelve: Python object persistence."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code></a>. The <a class="reference internal" href="#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 exists mainly to support reading and writing the “pseudo-compiled” code for Python modules of <code class="file docutils literal notranslate"><span class="pre">.pyc</span></code> files. Therefore, the Python maintainers reserve the right to modify the marshal format in backward incompatible ways should the need arise. If you’re serializing and de-serializing Python objects, use the <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> module instead – the performance is comparable, version independence is guaranteed, and pickle supports a substantially wider range of objects than marshal.</p> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last">The <a class="reference internal" href="#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 is not intended to be secure against erroneous or maliciously constructed data. Never unmarshal data received from an untrusted or unauthenticated source.</p> </div> <p id="index-1">Not all Python object types are supported; in general, only objects whose value is independent from a particular invocation of Python can be written and read by this module. The following types are supported: booleans, integers, long integers, floating point numbers, complex numbers, strings, Unicode objects, tuples, lists, sets, frozensets, dictionaries, and code objects, where it should be understood that tuples, lists, sets, frozensets and dictionaries are only supported as long as the values contained therein are themselves supported; and recursive lists, sets and dictionaries should not be written (they will cause infinite loops). The singletons <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>, <a class="reference internal" href="constants.html#Ellipsis" title="Ellipsis"><code class="xref py py-const docutils literal notranslate"><span class="pre">Ellipsis</span></code></a> and <a class="reference internal" href="exceptions.html#exceptions.StopIteration" title="exceptions.StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a> can also be marshalled and unmarshalled.</p> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last">On machines where C’s <code class="docutils literal notranslate"><span class="pre">long</span> <span class="pre">int</span></code> type has more than 32 bits (such as the DEC Alpha), it is possible to create plain Python integers that are longer than 32 bits. If such an integer is marshaled and read back in on a machine where C’s <code class="docutils literal notranslate"><span class="pre">long</span> <span class="pre">int</span></code> type has only 32 bits, a Python long integer object is returned instead. While of a different type, the numeric value is the same. (This behavior is new in Python 2.2. In earlier versions, all but the least-significant 32 bits of the value were lost, and a warning message was printed.)</p> </div> <p>There are functions that read/write files as well as functions operating on strings.</p> <p>The module defines these functions:</p> <dl class="function"> <dt id="marshal.dump"> <code class="descclassname">marshal.</code><code class="descname">dump</code><span class="sig-paren">(</span><em>value</em>, <em>file</em><span class="optional">[</span>, <em>version</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#marshal.dump" title="Permalink to this definition">¶</a></dt> <dd><p>Write the value on the open file. The value must be a supported type. The file must be an open file object such as <code class="docutils literal notranslate"><span class="pre">sys.stdout</span></code> or returned by <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> or <a class="reference internal" href="os.html#os.popen" title="os.popen"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.popen()</span></code></a>. It may not be a wrapper such as TemporaryFile on Windows. It must be opened in binary mode (<code class="docutils literal notranslate"><span class="pre">'wb'</span></code> or <code class="docutils literal notranslate"><span class="pre">'w+b'</span></code>).</p> <p>If the value has (or contains an object that has) an unsupported type, a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> exception is raised — but garbage data will also be written to the file. The object will not be properly read back by <a class="reference internal" href="#marshal.load" title="marshal.load"><code class="xref py py-func docutils literal notranslate"><span class="pre">load()</span></code></a>.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.4: </span>The <em>version</em> argument indicates the data format that <code class="docutils literal notranslate"><span class="pre">dump</span></code> should use (see below).</p> </div> </dd></dl> <dl class="function"> <dt id="marshal.load"> <code class="descclassname">marshal.</code><code class="descname">load</code><span class="sig-paren">(</span><em>file</em><span class="sig-paren">)</span><a class="headerlink" href="#marshal.load" title="Permalink to this definition">¶</a></dt> <dd><p>Read one value from the open file and return it. If no valid value is read (e.g. because the data has a different Python version’s incompatible marshal format), raise <a class="reference internal" href="exceptions.html#exceptions.EOFError" title="exceptions.EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>, <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> or <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>. The file must be an open file object opened in binary mode (<code class="docutils literal notranslate"><span class="pre">'rb'</span></code> or <code class="docutils literal notranslate"><span class="pre">'r+b'</span></code>).</p> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">If an object containing an unsupported type was marshalled with <a class="reference internal" href="#marshal.dump" title="marshal.dump"><code class="xref py py-func docutils literal notranslate"><span class="pre">dump()</span></code></a>, <a class="reference internal" href="#marshal.load" title="marshal.load"><code class="xref py py-func docutils literal notranslate"><span class="pre">load()</span></code></a> will substitute <code class="docutils literal notranslate"><span class="pre">None</span></code> for the unmarshallable type.</p> </div> </dd></dl> <dl class="function"> <dt id="marshal.dumps"> <code class="descclassname">marshal.</code><code class="descname">dumps</code><span class="sig-paren">(</span><em>value</em><span class="optional">[</span>, <em>version</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#marshal.dumps" title="Permalink to this definition">¶</a></dt> <dd><p>Return the string that would be written to a file by <code class="docutils literal notranslate"><span class="pre">dump(value,</span> <span class="pre">file)</span></code>. The value must be a supported type. Raise a <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> exception if value has (or contains an object that has) an unsupported type.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.4: </span>The <em>version</em> argument indicates the data format that <code class="docutils literal notranslate"><span class="pre">dumps</span></code> should use (see below).</p> </div> </dd></dl> <dl class="function"> <dt id="marshal.loads"> <code class="descclassname">marshal.</code><code class="descname">loads</code><span class="sig-paren">(</span><em>string</em><span class="sig-paren">)</span><a class="headerlink" href="#marshal.loads" title="Permalink to this definition">¶</a></dt> <dd><p>Convert the string to a value. If no valid value is found, raise <a class="reference internal" href="exceptions.html#exceptions.EOFError" title="exceptions.EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>, <a class="reference internal" href="exceptions.html#exceptions.ValueError" title="exceptions.ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> or <a class="reference internal" href="exceptions.html#exceptions.TypeError" title="exceptions.TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>. Extra characters in the string are ignored.</p> </dd></dl> <p>In addition, the following constants are defined:</p> <dl class="data"> <dt id="marshal.version"> <code class="descclassname">marshal.</code><code class="descname">version</code><a class="headerlink" href="#marshal.version" title="Permalink to this definition">¶</a></dt> <dd><p>Indicates the format that the module uses. Version 0 is the historical format, version 1 (added in Python 2.4) shares interned strings and version 2 (added in Python 2.5) uses a binary format for floating point numbers. The current version is 2.</p> <div class="versionadded"> <p><span class="versionmodified">New in version 2.4.</span></p> </div> </dd></dl> <p class="rubric">Footnotes</p> <table class="docutils footnote" frame="void" id="id2" rules="none"> <colgroup><col class="label" /><col /></colgroup> <tbody valign="top"> <tr><td class="label"><a class="fn-backref" href="#id1">[1]</a></td><td>The name of this module stems from a bit of terminology used by the designers of Modula-3 (amongst others), who use the term “marshalling” for shipping of data around in a self-contained form. Strictly speaking, “to marshal” means to convert some data from internal to external form (in an RPC buffer for instance) and “unmarshalling” for the reverse process.</td></tr> </tbody> </table> </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="shelve.html" title="previous chapter">11.4. <code class="docutils literal notranslate"><span class="pre">shelve</span></code> — Python object persistence</a></p> <h4>Next topic</h4> <p class="topless"><a href="anydbm.html" title="next chapter">11.6. <code class="docutils literal notranslate"><span class="pre">anydbm</span></code> — Generic access to DBM-style databases</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/library/marshal.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3>Quick search</h3> <div class="searchformwrapper"> <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> </div> </div> <script type="text/javascript">$('#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="anydbm.html" title="11.6. anydbm — Generic access to DBM-style databases" >next</a> |</li> <li class="right" > <a href="shelve.html" title="11.4. shelve — Python object persistence" >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="persistence.html" >11. 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