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<div class="section" id="data-persistence">
<span id="persistence"></span><h1>12. Data Persistence<a class="headerlink" href="#data-persistence" title="Permalink to this headline">¶</a></h1>
<p>The modules described in this chapter support storing Python data in a
persistent form on disk. 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> and <a class="reference internal" href="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> modules can turn
many Python data types into a stream of bytes and then recreate the objects from
the bytes. The various DBM-related modules support a family of hash-based file
formats that store a mapping of strings to other strings.</p>
<p>The list of modules described in this chapter is:</p>
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<li class="toctree-l1"><a class="reference internal" href="pickle.html">12.1. <code class="docutils literal notranslate"><span class="pre">pickle</span></code> — Python object serialization</a><ul>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#relationship-to-other-python-modules">12.1.1. Relationship to other Python modules</a><ul>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#comparison-with-marshal">12.1.1.1. Comparison with <code class="docutils literal notranslate"><span class="pre">marshal</span></code></a></li>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#comparison-with-json">12.1.1.2. Comparison with <code class="docutils literal notranslate"><span class="pre">json</span></code></a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#data-stream-format">12.1.2. Data stream format</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#module-interface">12.1.3. Module Interface</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#what-can-be-pickled-and-unpickled">12.1.4. What can be pickled and unpickled?</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#pickling-class-instances">12.1.5. Pickling Class Instances</a><ul>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#persistence-of-external-objects">12.1.5.1. Persistence of External Objects</a></li>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#dispatch-tables">12.1.5.2. Dispatch Tables</a></li>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#handling-stateful-objects">12.1.5.3. Handling Stateful Objects</a></li>
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<li class="toctree-l2"><a class="reference internal" href="pickle.html#restricting-globals">12.1.6. Restricting Globals</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#performance">12.1.7. Performance</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#examples">12.1.8. Examples</a></li>
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<li class="toctree-l1"><a class="reference internal" href="copyreg.html">12.2. <code class="docutils literal notranslate"><span class="pre">copyreg</span></code> — Register <code class="docutils literal notranslate"><span class="pre">pickle</span></code> support functions</a><ul>
<li class="toctree-l2"><a class="reference internal" href="copyreg.html#example">12.2.1. Example</a></li>
</ul>
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<li class="toctree-l1"><a class="reference internal" href="shelve.html">12.3. <code class="docutils literal notranslate"><span class="pre">shelve</span></code> — Python object persistence</a><ul>
<li class="toctree-l2"><a class="reference internal" href="shelve.html#restrictions">12.3.1. Restrictions</a></li>
<li class="toctree-l2"><a class="reference internal" href="shelve.html#example">12.3.2. Example</a></li>
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<li class="toctree-l1"><a class="reference internal" href="marshal.html">12.4. <code class="docutils literal notranslate"><span class="pre">marshal</span></code> — Internal Python object serialization</a></li>
<li class="toctree-l1"><a class="reference internal" href="dbm.html">12.5. <code class="docutils literal notranslate"><span class="pre">dbm</span></code> — Interfaces to Unix “databases”</a><ul>
<li class="toctree-l2"><a class="reference internal" href="dbm.html#module-dbm.gnu">12.5.1. <code class="docutils literal notranslate"><span class="pre">dbm.gnu</span></code> — GNU’s reinterpretation of dbm</a></li>
<li class="toctree-l2"><a class="reference internal" href="dbm.html#module-dbm.ndbm">12.5.2. <code class="docutils literal notranslate"><span class="pre">dbm.ndbm</span></code> — Interface based on ndbm</a></li>
<li class="toctree-l2"><a class="reference internal" href="dbm.html#module-dbm.dumb">12.5.3. <code class="docutils literal notranslate"><span class="pre">dbm.dumb</span></code> — Portable DBM implementation</a></li>
</ul>
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<li class="toctree-l1"><a class="reference internal" href="sqlite3.html">12.6. <code class="docutils literal notranslate"><span class="pre">sqlite3</span></code> — DB-API 2.0 interface for SQLite databases</a><ul>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#module-functions-and-constants">12.6.1. Module functions and constants</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#connection-objects">12.6.2. Connection Objects</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#cursor-objects">12.6.3. Cursor Objects</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#row-objects">12.6.4. Row Objects</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#exceptions">12.6.5. Exceptions</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#sqlite-and-python-types">12.6.6. SQLite and Python types</a><ul>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#introduction">12.6.6.1. Introduction</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#using-adapters-to-store-additional-python-types-in-sqlite-databases">12.6.6.2. Using adapters to store additional Python types in SQLite databases</a><ul>
<li class="toctree-l4"><a class="reference internal" href="sqlite3.html#letting-your-object-adapt-itself">12.6.6.2.1. Letting your object adapt itself</a></li>
<li class="toctree-l4"><a class="reference internal" href="sqlite3.html#registering-an-adapter-callable">12.6.6.2.2. Registering an adapter callable</a></li>
</ul>
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<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#converting-sqlite-values-to-custom-python-types">12.6.6.3. Converting SQLite values to custom Python types</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#default-adapters-and-converters">12.6.6.4. Default adapters and converters</a></li>
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<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#controlling-transactions">12.6.7. Controlling Transactions</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#using-sqlite3-efficiently">12.6.8. Using <code class="docutils literal notranslate"><span class="pre">sqlite3</span></code> efficiently</a><ul>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#using-shortcut-methods">12.6.8.1. Using shortcut methods</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#accessing-columns-by-name-instead-of-by-index">12.6.8.2. Accessing columns by name instead of by index</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#using-the-connection-as-a-context-manager">12.6.8.3. Using the connection as a context manager</a></li>
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<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#common-issues">12.6.9. Common issues</a><ul>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#multithreading">12.6.9.1. Multithreading</a></li>
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