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  <section id="data-persistence">
<span id="persistence"></span><h1>Data Persistence<a class="headerlink" href="#data-persistence" title="Link to this heading">¶</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#custom-reduction-for-types-functions-and-other-objects">Custom Reduction for Types, Functions, and Other Objects</a></li>
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<li class="toctree-l3"><a class="reference internal" href="pickle.html#provider-api">Provider API</a></li>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#consumer-api">Consumer API</a></li>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#example">Example</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>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#examples">Examples</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 database manager</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> — New Database Manager</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>
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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#tutorial">Tutorial</a></li>
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<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#how-to-use-placeholders-to-bind-values-in-sql-queries">How to use placeholders to bind values in SQL queries</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#how-to-adapt-custom-python-types-to-sqlite-values">How to adapt custom Python types to SQLite values</a><ul>
<li class="toctree-l4"><a class="reference internal" href="sqlite3.html#how-to-write-adaptable-objects">How to write adaptable objects</a></li>
<li class="toctree-l4"><a class="reference internal" href="sqlite3.html#how-to-register-adapter-callables">How to register adapter callables</a></li>
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<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#how-to-convert-sqlite-values-to-custom-python-types">How to convert SQLite values to custom Python types</a></li>
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<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#how-to-use-the-connection-context-manager">How to use the connection context manager</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#how-to-work-with-sqlite-uris">How to work with SQLite URIs</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#how-to-create-and-use-row-factories">How to create and use row factories</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#how-to-handle-non-utf-8-text-encodings">How to handle non-UTF-8 text encodings</a></li>
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<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#explanation">Explanation</a><ul>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#transaction-control">Transaction control</a><ul>
<li class="toctree-l4"><a class="reference internal" href="sqlite3.html#transaction-control-via-the-autocommit-attribute">Transaction control via the <code class="docutils literal notranslate"><span class="pre">autocommit</span></code> attribute</a></li>
<li class="toctree-l4"><a class="reference internal" href="sqlite3.html#transaction-control-via-the-isolation-level-attribute">Transaction control via the <code class="docutils literal notranslate"><span class="pre">isolation_level</span></code> attribute</a></li>
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