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<div class="section" id="module-dbhash">
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<span id="dbhash-dbm-style-interface-to-the-bsd-database-library"></span><h1>11.10. <a class="reference internal" href="#module-dbhash" title="dbhash: DBM-style interface to the BSD database library."><code class="xref py py-mod docutils literal"><span class="pre">dbhash</span></code></a> — DBM-style interface to the BSD database library<a class="headerlink" href="#module-dbhash" title="Permalink to this headline">¶</a></h1>
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<div class="deprecated">
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<p><span class="versionmodified">Deprecated since version 2.6: </span>The <a class="reference internal" href="#module-dbhash" title="dbhash: DBM-style interface to the BSD database library."><code class="xref py py-mod docutils literal"><span class="pre">dbhash</span></code></a> module has been removed in Python 3.</p>
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<p id="index-0">The <a class="reference internal" href="#module-dbhash" title="dbhash: DBM-style interface to the BSD database library."><code class="xref py py-mod docutils literal"><span class="pre">dbhash</span></code></a> module provides a function to open databases using the BSD
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<code class="docutils literal"><span class="pre">db</span></code> library. This module mirrors the interface of the other Python database
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modules that provide access to DBM-style databases. 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"><span class="pre">bsddb</span></code></a> module is
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required to use <a class="reference internal" href="#module-dbhash" title="dbhash: DBM-style interface to the BSD database library."><code class="xref py py-mod docutils literal"><span class="pre">dbhash</span></code></a>.</p>
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<p>This module provides an exception and a function:</p>
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<dl class="exception">
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<dt id="dbhash.error">
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<em class="property">exception </em><code class="descclassname">dbhash.</code><code class="descname">error</code><a class="headerlink" href="#dbhash.error" title="Permalink to this definition">¶</a></dt>
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<dd><p>Exception raised on database errors other than <a class="reference internal" href="exceptions.html#exceptions.KeyError" title="exceptions.KeyError"><code class="xref py py-exc docutils literal"><span class="pre">KeyError</span></code></a>. It is a synonym
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for <code class="xref py py-exc docutils literal"><span class="pre">bsddb.error</span></code>.</p>
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<code class="descclassname">dbhash.</code><code class="descname">open</code><span class="sig-paren">(</span><em>path</em><span class="optional">[</span>, <em>flag</em><span class="optional">[</span>, <em>mode</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#dbhash.open" title="Permalink to this definition">¶</a></dt>
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<dd><p>Open a <code class="docutils literal"><span class="pre">db</span></code> database and return the database object. The <em>path</em> argument is
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the name of the database file.</p>
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<p>The <em>flag</em> argument can be:</p>
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<table border="1" class="docutils">
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<thead valign="bottom">
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<tr class="row-odd"><th class="head">Value</th>
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<th class="head">Meaning</th>
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<tr class="row-even"><td><code class="docutils literal"><span class="pre">'r'</span></code></td>
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<td>Open existing database for reading only
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<tr class="row-odd"><td><code class="docutils literal"><span class="pre">'w'</span></code></td>
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<td>Open existing database for reading and
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<tr class="row-even"><td><code class="docutils literal"><span class="pre">'c'</span></code></td>
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<td>Open database for reading and writing,
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creating it if it doesn’t exist</td>
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<tr class="row-odd"><td><code class="docutils literal"><span class="pre">'n'</span></code></td>
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<td>Always create a new, empty database, open
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for reading and writing</td>
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<p>For platforms on which the BSD <code class="docutils literal"><span class="pre">db</span></code> library supports locking, an <code class="docutils literal"><span class="pre">'l'</span></code>
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can be appended to indicate that locking should be used.</p>
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<p>The optional <em>mode</em> parameter is used to indicate the Unix permission bits that
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should be set if a new database must be created; this will be masked by the
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current umask value for the process.</p>
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<div class="admonition seealso">
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<p class="first admonition-title">See also</p>
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<dl class="last docutils">
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<dt>Module <a class="reference internal" href="anydbm.html#module-anydbm" title="anydbm: Generic interface to DBM-style database modules."><code class="xref py py-mod docutils literal"><span class="pre">anydbm</span></code></a></dt>
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<dd>Generic interface to <code class="docutils literal"><span class="pre">dbm</span></code>-style databases.</dd>
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<dt>Module <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"><span class="pre">bsddb</span></code></a></dt>
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<dd>Lower-level interface to the BSD <code class="docutils literal"><span class="pre">db</span></code> library.</dd>
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<dt>Module <a class="reference internal" href="whichdb.html#module-whichdb" title="whichdb: Guess which DBM-style module created a given database."><code class="xref py py-mod docutils literal"><span class="pre">whichdb</span></code></a></dt>
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<dd>Utility module used to determine the type of an existing database.</dd>
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<div class="section" id="database-objects">
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<span id="dbhash-objects"></span><h2>11.10.1. Database Objects<a class="headerlink" href="#database-objects" title="Permalink to this headline">¶</a></h2>
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<p>The database objects returned by <a class="reference internal" href="#dbhash.open" title="dbhash.open"><code class="xref py py-func docutils literal"><span class="pre">open()</span></code></a> provide the methods common to all
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the DBM-style databases and mapping objects. The following methods are
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available in addition to the standard methods.</p>
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<dt id="dbhash.dbhash.first">
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<code class="descclassname">dbhash.</code><code class="descname">first</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#dbhash.dbhash.first" title="Permalink to this definition">¶</a></dt>
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<dd><p>It’s possible to loop over every key/value pair in the database using this
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method and the <code class="xref py py-meth docutils literal"><span class="pre">next()</span></code> method. The traversal is ordered by the databases
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internal hash values, and won’t be sorted by the key values. This method
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returns the starting key.</p>
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<dt id="dbhash.dbhash.last">
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<code class="descclassname">dbhash.</code><code class="descname">last</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#dbhash.dbhash.last" title="Permalink to this definition">¶</a></dt>
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<dd><p>Return the last key/value pair in a database traversal. This may be used to
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begin a reverse-order traversal; see <a class="reference internal" href="#dbhash.dbhash.previous" title="dbhash.dbhash.previous"><code class="xref py py-meth docutils literal"><span class="pre">previous()</span></code></a>.</p>
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<dt id="dbhash.dbhash.next">
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<code class="descclassname">dbhash.</code><code class="descname">next</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#dbhash.dbhash.next" title="Permalink to this definition">¶</a></dt>
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<dd><p>Returns the key next key/value pair in a database traversal. The following code
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prints every key in the database <code class="docutils literal"><span class="pre">db</span></code>, without having to create a list in
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memory that contains them all:</p>
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<div class="highlight-python"><div class="highlight"><pre><span class="k">print</span> <span class="n">db</span><span class="o">.</span><span class="n">first</span><span class="p">()</span>
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<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">xrange</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="n">db</span><span class="p">)):</span>
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<span class="k">print</span> <span class="n">db</span><span class="o">.</span><span class="n">next</span><span class="p">()</span>
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<dt id="dbhash.dbhash.previous">
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<code class="descclassname">dbhash.</code><code class="descname">previous</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#dbhash.dbhash.previous" title="Permalink to this definition">¶</a></dt>
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<dd><p>Returns the previous key/value pair in a forward-traversal of the database. In
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conjunction with <a class="reference internal" href="#dbhash.dbhash.last" title="dbhash.dbhash.last"><code class="xref py py-meth docutils literal"><span class="pre">last()</span></code></a>, this may be used to implement a reverse-order
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<dt id="dbhash.dbhash.sync">
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<code class="descclassname">dbhash.</code><code class="descname">sync</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#dbhash.dbhash.sync" title="Permalink to this definition">¶</a></dt>
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<dd><p>This method forces any unwritten data to be written to the disk.</p>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
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<li><a class="reference internal" href="#">11.10. <code class="docutils literal"><span class="pre">dbhash</span></code> — DBM-style interface to the BSD database library</a><ul>
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<li><a class="reference internal" href="#database-objects">11.10.1. Database Objects</a></li>
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<h4>Previous topic</h4>
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title="previous chapter">11.9. <code class="docutils literal"><span class="pre">gdbm</span></code> — GNU’s reinterpretation of dbm</a></p>
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title="next chapter">11.11. <code class="docutils literal"><span class="pre">bsddb</span></code> — Interface to Berkeley DB library</a></p>
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