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<div class="section" id="data-persistence">
<span id="persistence"></span><h1>11. 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. The <a class="reference internal" href="bsddb.html#module-bsddb" title="bsddb: Interface to Berkeley DB database library"><code class="xref py py-mod docutils literal notranslate"><span class="pre">bsddb</span></code></a>
module also provides such disk-based string-to-string mappings based on hashing,
and also supports B-Tree and record-based formats.</p>
<p>The list of modules described in this chapter is:</p>
<div class="toctree-wrapper compound">
<ul>
<li class="toctree-l1"><a class="reference internal" href="pickle.html">11.1. <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">11.1.1. Relationship to other Python modules</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#data-stream-format">11.1.2. Data stream format</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#usage">11.1.3. Usage</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#what-can-be-pickled-and-unpickled">11.1.4. What can be pickled and unpickled?</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#the-pickle-protocol">11.1.5. The pickle protocol</a><ul>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#pickling-and-unpickling-normal-class-instances">11.1.5.1. Pickling and unpickling normal class instances</a></li>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#pickling-and-unpickling-extension-types">11.1.5.2. Pickling and unpickling extension types</a></li>
<li class="toctree-l3"><a class="reference internal" href="pickle.html#pickling-and-unpickling-external-objects">11.1.5.3. Pickling and unpickling external objects</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#subclassing-unpicklers">11.1.6. Subclassing Unpicklers</a></li>
<li class="toctree-l2"><a class="reference internal" href="pickle.html#example">11.1.7. Example</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="pickle.html#module-cPickle">11.2. <code class="xref py py-mod docutils literal notranslate"><span class="pre">cPickle</span></code> — A faster <code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a></li>
<li class="toctree-l1"><a class="reference internal" href="copy_reg.html">11.3. <code class="xref py py-mod docutils literal notranslate"><span class="pre">copy_reg</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="copy_reg.html#example">11.3.1. Example</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="shelve.html">11.4. <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">11.4.1. Restrictions</a></li>
<li class="toctree-l2"><a class="reference internal" href="shelve.html#example">11.4.2. Example</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="marshal.html">11.5. <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="anydbm.html">11.6. <code class="xref py py-mod docutils literal notranslate"><span class="pre">anydbm</span></code> — Generic access to DBM-style databases</a></li>
<li class="toctree-l1"><a class="reference internal" href="whichdb.html">11.7. <code class="xref py py-mod docutils literal notranslate"><span class="pre">whichdb</span></code> — Guess which DBM module created a database</a></li>
<li class="toctree-l1"><a class="reference internal" href="dbm.html">11.8. <code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm</span></code> — Simple “database” interface</a></li>
<li class="toctree-l1"><a class="reference internal" href="gdbm.html">11.9. <code class="xref py py-mod docutils literal notranslate"><span class="pre">gdbm</span></code> — GNU’s reinterpretation of dbm</a></li>
<li class="toctree-l1"><a class="reference internal" href="dbhash.html">11.10. <code class="xref py py-mod docutils literal notranslate"><span class="pre">dbhash</span></code> — DBM-style interface to the BSD database library</a><ul>
<li class="toctree-l2"><a class="reference internal" href="dbhash.html#database-objects">11.10.1. Database Objects</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="bsddb.html">11.11. <code class="xref py py-mod docutils literal notranslate"><span class="pre">bsddb</span></code> — Interface to Berkeley DB library</a><ul>
<li class="toctree-l2"><a class="reference internal" href="bsddb.html#hash-btree-and-record-objects">11.11.1. Hash, BTree and Record Objects</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="dumbdbm.html">11.12. <code class="xref py py-mod docutils literal notranslate"><span class="pre">dumbdbm</span></code> — Portable DBM implementation</a><ul>
<li class="toctree-l2"><a class="reference internal" href="dumbdbm.html#dumbdbm-objects">11.12.1. Dumbdbm Objects</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="sqlite3.html">11.13. <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">11.13.1. Module functions and constants</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#connection-objects">11.13.2. Connection Objects</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#cursor-objects">11.13.3. Cursor Objects</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#row-objects">11.13.4. Row Objects</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#sqlite-and-python-types">11.13.5. SQLite and Python types</a><ul>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#introduction">11.13.5.1. Introduction</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#using-adapters-to-store-additional-python-types-in-sqlite-databases">11.13.5.2. 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">11.13.5.2.1. Letting your object adapt itself</a></li>
<li class="toctree-l4"><a class="reference internal" href="sqlite3.html#registering-an-adapter-callable">11.13.5.2.2. Registering an adapter callable</a></li>
</ul>
</li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#converting-sqlite-values-to-custom-python-types">11.13.5.3. Converting SQLite values to custom Python types</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#default-adapters-and-converters">11.13.5.4. Default adapters and converters</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#controlling-transactions">11.13.6. Controlling Transactions</a></li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#using-sqlite3-efficiently">11.13.7. 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">11.13.7.1. Using shortcut methods</a></li>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#accessing-columns-by-name-instead-of-by-index">11.13.7.2. 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">11.13.7.3. Using the connection as a context manager</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="sqlite3.html#common-issues">11.13.8. Common issues</a><ul>
<li class="toctree-l3"><a class="reference internal" href="sqlite3.html#multithreading">11.13.8.1. Multithreading</a></li>
</ul>
</li>
</ul>
</li>
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