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<div class="section" id="data-marshalling-support">
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<span id="marshalling-utils"></span><h1>Data marshalling support<a class="headerlink" href="#data-marshalling-support" title="Permalink to this headline">¶</a></h1>
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<p>These routines allow C code to work with serialized objects using the same
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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"><span class="pre">marshal</span></code></a> module. There are functions to write data
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into the serialization format, and additional functions that can be used to
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read the data back. Files used to store marshalled data must be opened in
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<p>Numeric values are stored with the least significant byte first.</p>
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<p>The module supports two versions of the data format: version 0 is the
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historical version, version 1 shares interned strings in the file, and upon
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unmarshalling. Version 2 uses a binary format for floating point numbers.
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<em>Py_MARSHAL_VERSION</em> indicates the current file format (currently 2).</p>
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<dt id="c.PyMarshal_WriteLongToFile">
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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>
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<dd><p>Marshal a <code class="xref c c-type docutils literal"><span class="pre">long</span></code> integer, <em>value</em>, to <em>file</em>. This will only write
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the least-significant 32 bits of <em>value</em>; regardless of the size of the
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native <code class="xref c c-type docutils literal"><span class="pre">long</span></code> type. <em>version</em> indicates the file format.</p>
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<dt id="c.PyMarshal_WriteObjectToFile">
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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>
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<dd><p>Marshal a Python object, <em>value</em>, to <em>file</em>.
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<em>version</em> indicates the file format.</p>
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<dl class="function">
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<dt id="c.PyMarshal_WriteObjectToString">
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<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>
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<dd><em class="refcount">Return value: New reference.</em><p>Return a string object containing the marshalled representation of <em>value</em>.
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<em>version</em> indicates the file format.</p>
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<p>The following functions allow marshalled values to be read back in.</p>
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<p>XXX What about error detection? It appears that reading past the end of the
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file will always result in a negative numeric value (where that’s relevant),
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but it’s not clear that negative values won’t be handled properly when there’s
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no error. What’s the right way to tell? Should only non-negative values be
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written using these routines?</p>
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<dl class="function">
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<dt id="c.PyMarshal_ReadLongFromFile">
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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>
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<dd><p>Return a C <code class="xref c c-type docutils literal"><span class="pre">long</span></code> from the data stream in a <code class="xref c c-type docutils literal"><span class="pre">FILE*</span></code> opened
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for reading. Only a 32-bit value can be read in using this function,
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regardless of the native size of <code class="xref c c-type docutils literal"><span class="pre">long</span></code>.</p>
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<p>On error, raise an exception and return <code class="docutils literal"><span class="pre">-1</span></code>.</p>
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<dl class="function">
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<dt id="c.PyMarshal_ReadShortFromFile">
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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>
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<dd><p>Return a C <code class="xref c c-type docutils literal"><span class="pre">short</span></code> from the data stream in a <code class="xref c c-type docutils literal"><span class="pre">FILE*</span></code> opened
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for reading. Only a 16-bit value can be read in using this function,
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regardless of the native size of <code class="xref c c-type docutils literal"><span class="pre">short</span></code>.</p>
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<p>On error, raise an exception and return <code class="docutils literal"><span class="pre">-1</span></code>.</p>
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<dl class="function">
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<dt id="c.PyMarshal_ReadObjectFromFile">
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<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>
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<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"><span class="pre">FILE*</span></code> opened for
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<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"><span class="pre">EOFError</span></code></a> or
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<a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal"><span class="pre">TypeError</span></code></a>) and returns <em>NULL</em>.</p>
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<dl class="function">
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<dt id="c.PyMarshal_ReadLastObjectFromFile">
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<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>
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<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"><span class="pre">FILE*</span></code> opened for
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reading. Unlike <a class="reference internal" href="#c.PyMarshal_ReadObjectFromFile" title="PyMarshal_ReadObjectFromFile"><code class="xref c c-func docutils literal"><span class="pre">PyMarshal_ReadObjectFromFile()</span></code></a>, this function
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assumes that no further objects will be read from the file, allowing it to
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aggressively load file data into memory so that the de-serialization can
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operate from data in memory rather than reading a byte at a time from the
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file. Only use these variant if you are certain that you won’t be reading
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anything else from the file.</p>
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<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"><span class="pre">EOFError</span></code></a> or
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<a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal"><span class="pre">TypeError</span></code></a>) and returns <em>NULL</em>.</p>
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<dl class="function">
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<dt id="c.PyMarshal_ReadObjectFromString">
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<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> *string</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>
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<dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a character buffer
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containing <em>len</em> bytes pointed to by <em>string</em>.</p>
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<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"><span class="pre">EOFError</span></code></a> or
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<a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal"><span class="pre">TypeError</span></code></a>) and returns <em>NULL</em>.</p>
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