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<section id="module-marshal">
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<span id="marshal-internal-python-object-serialization"></span><h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">marshal</span></code> — Internal Python object serialization<a class="headerlink" href="#module-marshal" title="Link to this heading">¶</a></h1>
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<hr class="docutils" />
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<p>This module contains functions that can read and write Python values in a binary
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format. The format is specific to Python, but independent of machine
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architecture issues (e.g., you can write a Python value to a file on a PC,
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transport the file to a Mac, and read it back there). Details of the format are
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undocumented on purpose; it may change between Python versions (although it
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rarely does). <a class="footnote-reference brackets" href="#id2" id="id1" role="doc-noteref"><span class="fn-bracket">[</span>1<span class="fn-bracket">]</span></a></p>
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<p id="index-0">This is not a general “persistence” module. For general persistence and
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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
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<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 <code class="xref py py-mod docutils literal notranslate"><span class="pre">marshal</span></code> 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.
|
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Therefore, the Python maintainers reserve the right to modify the marshal format
|
||
in backward incompatible ways should the need arise.
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||
The format of code objects is not compatible between Python versions,
|
||
even if the version of the format is the same.
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||
De-serializing a code object in the incorrect Python version has undefined behavior.
|
||
If you’re serializing and
|
||
de-serializing Python objects, use the <code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code> module instead – the
|
||
performance is comparable, version independence is guaranteed, and pickle
|
||
supports a substantially wider range of objects than marshal.</p>
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<div class="admonition warning">
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<p class="admonition-title">Warning</p>
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<p>The <code class="xref py py-mod docutils literal notranslate"><span class="pre">marshal</span></code> module is not intended to be secure against erroneous or
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maliciously constructed data. Never unmarshal data received from an
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untrusted or unauthenticated source.</p>
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</div>
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<p>There are functions that read/write files as well as functions operating on
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bytes-like objects.</p>
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||
<p id="index-1">Not all Python object types are supported; in general, only objects whose value
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is independent from a particular invocation of Python can be written and read by
|
||
this module. The following types are supported:</p>
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||
<ul class="simple">
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||
<li><p>Numeric types: <a class="reference internal" href="../builtins/functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>, <a class="reference internal" href="../builtins/functions.html#bool" title="bool"><code class="xref py py-class docutils literal notranslate"><span class="pre">bool</span></code></a>, <a class="reference internal" href="../builtins/functions.html#float" title="float"><code class="xref py py-class docutils literal notranslate"><span class="pre">float</span></code></a>, <a class="reference internal" href="../builtins/functions.html#complex" title="complex"><code class="xref py py-class docutils literal notranslate"><span class="pre">complex</span></code></a>.</p></li>
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||
<li><p>Strings (<a class="reference internal" href="../builtins/stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>) and <a class="reference internal" href="../builtins/stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>.
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<a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">Bytes-like objects</span></a> like <a class="reference internal" href="../builtins/stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytearray</span></code></a> are
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marshalled as <code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code>.</p></li>
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<li><p>Containers: <a class="reference internal" href="../builtins/stdtypes.html#tuple" title="tuple"><code class="xref py py-class docutils literal notranslate"><span class="pre">tuple</span></code></a>, <a class="reference internal" href="../builtins/stdtypes.html#list" title="list"><code class="xref py py-class docutils literal notranslate"><span class="pre">list</span></code></a>, <a class="reference internal" href="../builtins/stdtypes.html#dict" title="dict"><code class="xref py py-class docutils literal notranslate"><span class="pre">dict</span></code></a>, <a class="reference internal" href="../builtins/stdtypes.html#frozendict" title="frozendict"><code class="xref py py-class docutils literal notranslate"><span class="pre">frozendict</span></code></a>
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(since <a class="reference internal" href="#marshal.version" title="marshal.version"><code class="xref py py-data docutils literal notranslate"><span class="pre">version</span></code></a> 6), <a class="reference internal" href="../builtins/stdtypes.html#set" title="set"><code class="xref py py-class docutils literal notranslate"><span class="pre">set</span></code></a>, <a class="reference internal" href="../builtins/stdtypes.html#frozenset" title="frozenset"><code class="xref py py-class docutils literal notranslate"><span class="pre">frozenset</span></code></a>, and
|
||
<a class="reference internal" href="../builtins/functions.html#slice" title="slice"><code class="xref py py-class docutils literal notranslate"><span class="pre">slice</span></code></a> (since <code class="xref py py-data docutils literal notranslate"><span class="pre">version</span></code> 5).
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It should be understood that these are supported only if the values contained
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therein are themselves supported.
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Recursive containers are supported since <code class="xref py py-data docutils literal notranslate"><span class="pre">version</span></code> 3.</p></li>
|
||
<li><p>The singletons <a class="reference internal" href="../builtins/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="../builtins/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="../builtins/exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate"><span class="pre">StopIteration</span></code></a>.</p></li>
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||
<li><p><a class="reference internal" href="code.html#module-code" title="code: Facilities to implement read-eval-print loops."><code class="xref py py-class docutils literal notranslate"><span class="pre">code</span></code></a> objects, if <em>allow_code</em> is true. See note above about
|
||
version dependence.</p></li>
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</ul>
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<div class="versionchanged">
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<p><span class="versionmodified changed">Changed in version 3.4: </span></p>
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<ul class="simple">
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<li><p>Added format version 3, which supports marshalling recursive lists, sets
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and dictionaries.</p></li>
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<li><p>Added format version 4, which supports efficient representations
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of short strings.</p></li>
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</ul>
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</div>
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<div class="versionchanged">
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<p><span class="versionmodified changed">Changed in version 3.14: </span>Added format version 5, which allows marshalling slices.</p>
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</div>
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<div class="versionchanged">
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||
<p><span class="versionmodified changed">Changed in version 3.15: </span>Added format version 6, which allows marshalling <a class="reference internal" href="../builtins/stdtypes.html#frozendict" title="frozendict"><code class="xref py py-class docutils literal notranslate"><span class="pre">frozendict</span></code></a>.</p>
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</div>
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<p>The module defines these functions:</p>
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<dl class="py function">
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||
<dt class="sig sig-object py" id="marshal.dump">
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||
<span class="sig-prename descclassname"><span class="pre">marshal.</span></span><span class="sig-name descname"><span class="pre">dump</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">file</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">version</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">version</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em>, <em class="sig-param"><span class="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">allow_code</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#marshal.dump" title="Link 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 a writeable <a class="reference internal" href="../glossary.html#term-binary-file"><span class="xref std std-term">binary file</span></a>.</p>
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||
<p>If the value has (or contains an object that has) an unsupported type, a
|
||
<a class="reference internal" href="../builtins/exceptions.html#ValueError" title="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>.
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||
<a class="reference internal" href="../reference/datamodel.html#code-objects"><span class="std std-ref">Code objects</span></a> are only supported if <em>allow_code</em> is true.</p>
|
||
<p>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>
|
||
<p class="audit-hook">Raises an <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">auditing event</span></a> <code class="docutils literal notranslate"><span class="pre">marshal.dumps</span></code> with arguments <code class="docutils literal notranslate"><span class="pre">value</span></code>, <code class="docutils literal notranslate"><span class="pre">version</span></code>.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.13: </span>Added the <em>allow_code</em> parameter.</p>
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||
</div>
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</dd></dl>
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|
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<dl class="py function">
|
||
<dt class="sig sig-object py" id="marshal.load">
|
||
<span class="sig-prename descclassname"><span class="pre">marshal.</span></span><span class="sig-name descname"><span class="pre">load</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">file</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em>, <em class="sig-param"><span class="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">allow_code</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#marshal.load" title="Link 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="../builtins/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="../builtins/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="../builtins/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.
|
||
<a class="reference internal" href="../reference/datamodel.html#code-objects"><span class="std std-ref">Code objects</span></a> are only supported if <em>allow_code</em> is true.
|
||
The file must be a readable <a class="reference internal" href="../glossary.html#term-binary-file"><span class="xref std std-term">binary file</span></a>.</p>
|
||
<p class="audit-hook">Raises an <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">auditing event</span></a> <code class="docutils literal notranslate"><span class="pre">marshal.load</span></code> with no arguments.</p>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>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>,
|
||
<code class="xref py py-func docutils literal notranslate"><span class="pre">load()</span></code> will substitute <code class="docutils literal notranslate"><span class="pre">None</span></code> for the unmarshallable type.</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.10: </span>This call used to raise a <code class="docutils literal notranslate"><span class="pre">code.__new__</span></code> audit event for each code object. Now
|
||
it raises a single <code class="docutils literal notranslate"><span class="pre">marshal.load</span></code> event for the entire load operation.</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.13: </span>Added the <em>allow_code</em> parameter.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="marshal.dumps">
|
||
<span class="sig-prename descclassname"><span class="pre">marshal.</span></span><span class="sig-name descname"><span class="pre">dumps</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">value</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">version</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">version</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em>, <em class="sig-param"><span class="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">allow_code</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#marshal.dumps" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Return the bytes object 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="../builtins/exceptions.html#ValueError" title="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.
|
||
<a class="reference internal" href="../reference/datamodel.html#code-objects"><span class="std std-ref">Code objects</span></a> are only supported if <em>allow_code</em> is true.</p>
|
||
<p>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>
|
||
<p class="audit-hook">Raises an <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">auditing event</span></a> <code class="docutils literal notranslate"><span class="pre">marshal.dumps</span></code> with arguments <code class="docutils literal notranslate"><span class="pre">value</span></code>, <code class="docutils literal notranslate"><span class="pre">version</span></code>.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.13: </span>Added the <em>allow_code</em> parameter.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="marshal.loads">
|
||
<span class="sig-prename descclassname"><span class="pre">marshal.</span></span><span class="sig-name descname"><span class="pre">loads</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">bytes</span></span></em>, <em class="sig-param"><span class="positional-only-separator o"><abbr title="Positional-only parameter separator (PEP 570)"><span class="pre">/</span></abbr></span></em>, <em class="sig-param"><span class="keyword-only-separator o"><abbr title="Keyword-only parameters separator (PEP 3102)"><span class="pre">*</span></abbr></span></em>, <em class="sig-param"><span class="n"><span class="pre">allow_code</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#marshal.loads" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Convert the <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a> to a value. If no valid value is found, raise
|
||
<a class="reference internal" href="../builtins/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="../builtins/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="../builtins/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>.
|
||
<a class="reference internal" href="../reference/datamodel.html#code-objects"><span class="std std-ref">Code objects</span></a> are only supported if <em>allow_code</em> is true.
|
||
Extra bytes in the input are ignored.</p>
|
||
<p class="audit-hook">Raises an <a class="reference internal" href="sys.html#auditing"><span class="std std-ref">auditing event</span></a> <code class="docutils literal notranslate"><span class="pre">marshal.loads</span></code> with argument <code class="docutils literal notranslate"><span class="pre">bytes</span></code>.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.10: </span>This call used to raise a <code class="docutils literal notranslate"><span class="pre">code.__new__</span></code> audit event for each code object. Now
|
||
it raises a single <code class="docutils literal notranslate"><span class="pre">marshal.loads</span></code> event for the entire load operation.</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.13: </span>Added the <em>allow_code</em> parameter.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<p>In addition, the following constants are defined:</p>
|
||
<dl class="py data">
|
||
<dt class="sig sig-object py" id="marshal.version">
|
||
<span class="sig-prename descclassname"><span class="pre">marshal.</span></span><span class="sig-name descname"><span class="pre">version</span></span><a class="headerlink" href="#marshal.version" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Indicates the format that the module uses.
|
||
Version 0 is the historical first version; subsequent versions
|
||
add new features.
|
||
Generally, a new version becomes the default when it is introduced.</p>
|
||
<table class="docutils align-default">
|
||
<thead>
|
||
<tr class="row-odd"><th class="head"><p>Version</p></th>
|
||
<th class="head"><p>Available since</p></th>
|
||
<th class="head"><p>New features</p></th>
|
||
</tr>
|
||
</thead>
|
||
<tbody>
|
||
<tr class="row-even"><td><p>1</p></td>
|
||
<td><p>Python 2.4</p></td>
|
||
<td><p>Sharing interned strings</p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p>2</p></td>
|
||
<td><p>Python 2.5</p></td>
|
||
<td><p>Binary representation of floats</p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p>3</p></td>
|
||
<td><p>Python 3.4</p></td>
|
||
<td><p>Support for object instancing and recursion</p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p>4</p></td>
|
||
<td><p>Python 3.4</p></td>
|
||
<td><p>Efficient representation of short strings</p></td>
|
||
</tr>
|
||
<tr class="row-even"><td><p>5</p></td>
|
||
<td><p>Python 3.14</p></td>
|
||
<td><p>Support for <a class="reference internal" href="../builtins/functions.html#slice" title="slice"><code class="xref py py-class docutils literal notranslate"><span class="pre">slice</span></code></a> objects</p></td>
|
||
</tr>
|
||
<tr class="row-odd"><td><p>6</p></td>
|
||
<td><p>Python 3.15</p></td>
|
||
<td><p>Support for <a class="reference internal" href="../builtins/stdtypes.html#frozendict" title="frozendict"><code class="xref py py-class docutils literal notranslate"><span class="pre">frozendict</span></code></a> objects</p></td>
|
||
</tr>
|
||
</tbody>
|
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</table>
|
||
</dd></dl>
|
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|
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<p class="rubric">Footnotes</p>
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<aside class="footnote-list brackets">
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|
||
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id1">1</a><span class="fn-bracket">]</span></span>
|
||
<p>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.</p>
|
||
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|
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