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<span id="persistence"></span><h1>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"><code class="xref py py-mod 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">Relationship to other Python modules</a><ul>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#comparison-with-marshal">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">Comparison with <code class="docutils literal notranslate"><span class="pre">json</span></code></a></li>
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<li class="toctree-l2"><a class="reference internal" href="pickle.html#data-stream-format">Data stream format</a></li>
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<li class="toctree-l2"><a class="reference internal" href="pickle.html#what-can-be-pickled-and-unpickled">What can be pickled and unpickled?</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#pickling-class-instances">Pickling Class Instances</a><ul>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#persistence-of-external-objects">Persistence of External Objects</a></li>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#dispatch-tables">Dispatch Tables</a></li>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#handling-stateful-objects">Handling Stateful Objects</a></li>
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<li class="toctree-l2"><a class="reference internal" href="pickle.html#restricting-globals">Restricting Globals</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#performance">Performance</a></li>
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<li class="toctree-l1"><a class="reference internal" href="copyreg.html"><code class="xref py py-mod docutils literal notranslate"><span class="pre">copyreg</span></code> — Register <code class="xref py py-mod 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">Example</a></li>
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<li class="toctree-l1"><a class="reference internal" href="shelve.html"><code class="xref py py-mod 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">Restrictions</a></li>
<li class="toctree-l2"><a class="reference internal" href="shelve.html#example">Example</a></li>
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<li class="toctree-l1"><a class="reference internal" href="marshal.html"><code class="xref py py-mod 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"><code class="xref py py-mod 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"><code class="xref py py-mod 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"><code class="xref py py-mod 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"><code class="xref py py-mod 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"><code class="xref py py-mod 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">Module functions and constants</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#connection-objects">Connection Objects</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#cursor-objects">Cursor Objects</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#row-objects">Row Objects</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#exceptions">Exceptions</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#sqlite-and-python-types">SQLite and Python types</a><ul>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#introduction">Introduction</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#using-adapters-to-store-additional-python-types-in-sqlite-databases">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">Letting your object adapt itself</a></li>
<li class="toctree-l4"><a class="reference internal" href="sqlite3.html#registering-an-adapter-callable">Registering an adapter callable</a></li>
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<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#converting-sqlite-values-to-custom-python-types">Converting SQLite values to custom Python types</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#default-adapters-and-converters">Default adapters and converters</a></li>
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<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#controlling-transactions">Controlling Transactions</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#using-sqlite3-efficiently">Using <code class="xref py py-mod 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">Using shortcut methods</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#accessing-columns-by-name-instead-of-by-index">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">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">Common issues</a><ul>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#multithreading">Multithreading</a></li>
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