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<div class="section" id="module-copyreg">
<span id="copyreg-register-pickle-support-functions"></span><h1>12.2. <a class="reference internal" href="#module-copyreg" title="copyreg: Register pickle support functions."><tt class="xref py py-mod docutils literal"><span class="pre">copyreg</span></tt></a> — Register <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><tt class="xref py py-mod docutils literal"><span class="pre">pickle</span></tt></a> support functions<a class="headerlink" href="#module-copyreg" title="Permalink to this headline">¶</a></h1>
<p id="index-0">The <a class="reference internal" href="#module-copyreg" title="copyreg: Register pickle support functions."><tt class="xref py py-mod docutils literal"><span class="pre">copyreg</span></tt></a> module offers a way to define fuctions used while pickling
specific objects. The <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><tt class="xref py py-mod docutils literal"><span class="pre">pickle</span></tt></a> and <a class="reference internal" href="copy.html#module-copy" title="copy: Shallow and deep copy operations."><tt class="xref py py-mod docutils literal"><span class="pre">copy</span></tt></a> modules use those functions
when pickling/copying those objects. The module provides configuration
information about object constructors which are not classes.
Such constructors may be factory functions or class instances.</p>
<dl class="function">
<dt id="copyreg.constructor">
<tt class="descclassname">copyreg.</tt><tt class="descname">constructor</tt><big>(</big><em>object</em><big>)</big><a class="headerlink" href="#copyreg.constructor" title="Permalink to this definition">¶</a></dt>
<dd><p>Declares <em>object</em> to be a valid constructor. If <em>object</em> is not callable (and
hence not valid as a constructor), raises <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a>.</p>
</dd></dl>
<dl class="function">
<dt id="copyreg.pickle">
<tt class="descclassname">copyreg.</tt><tt class="descname">pickle</tt><big>(</big><em>type</em>, <em>function</em>, <em>constructor=None</em><big>)</big><a class="headerlink" href="#copyreg.pickle" title="Permalink to this definition">¶</a></dt>
<dd><p>Declares that <em>function</em> should be used as a “reduction” function for objects
of type <em>type</em>. <em>function</em> should return either a string or a tuple
containing two or three elements.</p>
<p>The optional <em>constructor</em> parameter, if provided, is a callable object which
can be used to reconstruct the object when called with the tuple of arguments
returned by <em>function</em> at pickling time. <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><tt class="xref py py-exc docutils literal"><span class="pre">TypeError</span></tt></a> will be raised if
<em>object</em> is a class or <em>constructor</em> is not callable.</p>
<p>See the <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><tt class="xref py py-mod docutils literal"><span class="pre">pickle</span></tt></a> module for more details on the interface
expected of <em>function</em> and <em>constructor</em>. Note that the
<a class="reference internal" href="pickle.html#pickle.Pickler.dispatch_table" title="pickle.Pickler.dispatch_table"><tt class="xref py py-attr docutils literal"><span class="pre">dispatch_table</span></tt></a> attribute of a pickler
object or subclass of <a class="reference internal" href="pickle.html#pickle.Pickler" title="pickle.Pickler"><tt class="xref py py-class docutils literal"><span class="pre">pickle.Pickler</span></tt></a> can also be used for
declaring reduction functions.</p>
</dd></dl>
<div class="section" id="example">
<h2>12.2.1. Example<a class="headerlink" href="#example" title="Permalink to this headline">¶</a></h2>
<p>The example below would like to show how to register a pickle function and how
it will be used:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">copyreg</span><span class="o">,</span> <span class="nn">copy</span><span class="o">,</span> <span class="nn">pickle</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">a</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">a</span> <span class="o">=</span> <span class="n">a</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">def</span> <span class="nf">pickle_c</span><span class="p">(</span><span class="n">c</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s">"pickling a C instance..."</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">C</span><span class="p">,</span> <span class="p">(</span><span class="n">c</span><span class="o">.</span><span class="n">a</span><span class="p">,)</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">copyreg</span><span class="o">.</span><span class="n">pickle</span><span class="p">(</span><span class="n">C</span><span class="p">,</span> <span class="n">pickle_c</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">c</span> <span class="o">=</span> <span class="n">C</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">d</span> <span class="o">=</span> <span class="n">copy</span><span class="o">.</span><span class="n">copy</span><span class="p">(</span><span class="n">c</span><span class="p">)</span>
<span class="go">pickling a C instance...</span>
<span class="gp">>>> </span><span class="n">p</span> <span class="o">=</span> <span class="n">pickle</span><span class="o">.</span><span class="n">dumps</span><span class="p">(</span><span class="n">c</span><span class="p">)</span>
<span class="go">pickling a C instance...</span>
</pre></div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">12.2. <tt class="docutils literal"><span class="pre">copyreg</span></tt> — Register <tt class="docutils literal"><span class="pre">pickle</span></tt> support functions</a><ul>
<li><a class="reference internal" href="#example">12.2.1. Example</a></li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="pickle.html"
title="previous chapter">12.1. <tt class="docutils literal"><span class="pre">pickle</span></tt> — Python object serialization</a></p>
<h4>Next topic</h4>
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title="next chapter">12.3. <tt class="docutils literal"><span class="pre">shelve</span></tt> — Python object persistence</a></p>
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