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Data Persistence</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-dbhash"> <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."><tt class="xref py py-mod docutils literal"><span class="pre">dbhash</span></tt></a> — DBM-style interface to the BSD database library<a class="headerlink" href="#module-dbhash" title="Permalink to this headline">¶</a></h1> <p class="deprecated"> <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."><tt class="xref py py-mod docutils literal"><span class="pre">dbhash</span></tt></a> module has been removed in Python 3.</p> <p id="index-0">The <a class="reference internal" href="#module-dbhash" title="dbhash: DBM-style interface to the BSD database library."><tt class="xref py py-mod docutils literal"><span class="pre">dbhash</span></tt></a> module provides a function to open databases using the BSD <tt class="docutils literal"><span class="pre">db</span></tt> library. This module mirrors the interface of the other Python database 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"><tt class="xref py py-mod docutils literal"><span class="pre">bsddb</span></tt></a> module is required to use <a class="reference internal" href="#module-dbhash" title="dbhash: DBM-style interface to the BSD database library."><tt class="xref py py-mod docutils literal"><span class="pre">dbhash</span></tt></a>.</p> <p>This module provides an exception and a function:</p> <dl class="exception"> <dt id="dbhash.error"> <em class="property">exception </em><tt class="descclassname">dbhash.</tt><tt class="descname">error</tt><a class="headerlink" href="#dbhash.error" title="Permalink to this definition">¶</a></dt> <dd><p>Exception raised on database errors other than <a class="reference internal" href="exceptions.html#exceptions.KeyError" title="exceptions.KeyError"><tt class="xref py py-exc docutils literal"><span class="pre">KeyError</span></tt></a>. It is a synonym for <tt class="xref py py-exc docutils literal"><span class="pre">bsddb.error</span></tt>.</p> </dd></dl> <dl class="function"> <dt id="dbhash.open"> <tt class="descclassname">dbhash.</tt><tt class="descname">open</tt><big>(</big><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><big>)</big><a class="headerlink" href="#dbhash.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open a <tt class="docutils literal"><span class="pre">db</span></tt> database and return the database object. The <em>path</em> argument is the name of the database file.</p> <p>The <em>flag</em> argument can be:</p> <table border="1" class="docutils"> <colgroup> <col width="17%" /> <col width="83%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Value</th> <th class="head">Meaning</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">'r'</span></tt></td> <td>Open existing database for reading only (default)</td> </tr> <tr class="row-odd"><td><tt class="docutils literal"><span class="pre">'w'</span></tt></td> <td>Open existing database for reading and writing</td> </tr> <tr class="row-even"><td><tt class="docutils literal"><span class="pre">'c'</span></tt></td> <td>Open database for reading and writing, creating it if it doesn’t exist</td> </tr> <tr class="row-odd"><td><tt class="docutils literal"><span class="pre">'n'</span></tt></td> <td>Always create a new, empty database, open for reading and writing</td> </tr> </tbody> </table> <p>For platforms on which the BSD <tt class="docutils literal"><span class="pre">db</span></tt> library supports locking, an <tt class="docutils literal"><span class="pre">'l'</span></tt> can be appended to indicate that locking should be used.</p> <p>The optional <em>mode</em> parameter is used to indicate the Unix permission bits that should be set if a new database must be created; this will be masked by the current umask value for the process.</p> </dd></dl> <div class="admonition-see-also admonition seealso"> <p class="first admonition-title">See also</p> <dl class="last docutils"> <dt>Module <a class="reference internal" href="anydbm.html#module-anydbm" title="anydbm: Generic interface to DBM-style database modules."><tt class="xref py py-mod docutils literal"><span class="pre">anydbm</span></tt></a></dt> <dd>Generic interface to <tt class="docutils literal"><span class="pre">dbm</span></tt>-style databases.</dd> <dt>Module <a class="reference internal" href="bsddb.html#module-bsddb" title="bsddb: Interface to Berkeley DB database library"><tt class="xref py py-mod docutils literal"><span class="pre">bsddb</span></tt></a></dt> <dd>Lower-level interface to the BSD <tt class="docutils literal"><span class="pre">db</span></tt> library.</dd> <dt>Module <a class="reference internal" href="whichdb.html#module-whichdb" title="whichdb: Guess which DBM-style module created a given database."><tt class="xref py py-mod docutils literal"><span class="pre">whichdb</span></tt></a></dt> <dd>Utility module used to determine the type of an existing database.</dd> </dl> </div> <div class="section" id="database-objects"> <span id="dbhash-objects"></span><h2>11.10.1. Database Objects<a class="headerlink" href="#database-objects" title="Permalink to this headline">¶</a></h2> <p>The database objects returned by <a class="reference internal" href="#dbhash.open" title="dbhash.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> provide the methods common to all the DBM-style databases and mapping objects. The following methods are available in addition to the standard methods.</p> <dl class="method"> <dt id="dbhash.dbhash.first"> <tt class="descclassname">dbhash.</tt><tt class="descname">first</tt><big>(</big><big>)</big><a class="headerlink" href="#dbhash.dbhash.first" title="Permalink to this definition">¶</a></dt> <dd><p>It’s possible to loop over every key/value pair in the database using this method and the <tt class="xref py py-meth docutils literal"><span class="pre">next()</span></tt> method. The traversal is ordered by the databases internal hash values, and won’t be sorted by the key values. This method returns the starting key.</p> </dd></dl> <dl class="method"> <dt id="dbhash.dbhash.last"> <tt class="descclassname">dbhash.</tt><tt class="descname">last</tt><big>(</big><big>)</big><a class="headerlink" href="#dbhash.dbhash.last" title="Permalink to this definition">¶</a></dt> <dd><p>Return the last key/value pair in a database traversal. This may be used to begin a reverse-order traversal; see <a class="reference internal" href="#dbhash.dbhash.previous" title="dbhash.dbhash.previous"><tt class="xref py py-meth docutils literal"><span class="pre">previous()</span></tt></a>.</p> </dd></dl> <dl class="method"> <dt id="dbhash.dbhash.next"> <tt class="descclassname">dbhash.</tt><tt class="descname">next</tt><big>(</big><big>)</big><a class="headerlink" href="#dbhash.dbhash.next" title="Permalink to this definition">¶</a></dt> <dd><p>Returns the key next key/value pair in a database traversal. The following code prints every key in the database <tt class="docutils literal"><span class="pre">db</span></tt>, without having to create a list in memory that contains them all:</p> <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> <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> <span class="k">print</span> <span class="n">db</span><span class="o">.</span><span class="n">next</span><span class="p">()</span> </pre></div> </div> </dd></dl> <dl class="method"> <dt id="dbhash.dbhash.previous"> <tt class="descclassname">dbhash.</tt><tt class="descname">previous</tt><big>(</big><big>)</big><a class="headerlink" href="#dbhash.dbhash.previous" title="Permalink to this definition">¶</a></dt> <dd><p>Returns the previous key/value pair in a forward-traversal of the database. In conjunction with <a class="reference internal" href="#dbhash.dbhash.last" title="dbhash.dbhash.last"><tt class="xref py py-meth docutils literal"><span class="pre">last()</span></tt></a>, this may be used to implement a reverse-order traversal.</p> </dd></dl> <dl class="method"> <dt id="dbhash.dbhash.sync"> <tt class="descclassname">dbhash.</tt><tt class="descname">sync</tt><big>(</big><big>)</big><a class="headerlink" href="#dbhash.dbhash.sync" title="Permalink to this definition">¶</a></dt> <dd><p>This method forces any unwritten data to be written to the disk.</p> </dd></dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">11.10. <tt class="docutils literal"><span class="pre">dbhash</span></tt> — DBM-style interface to the BSD database library</a><ul> <li><a class="reference internal" href="#database-objects">11.10.1. Database Objects</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="gdbm.html" title="previous chapter">11.9. <tt class="docutils literal"><span class="pre">gdbm</span></tt> — GNU’s reinterpretation of dbm</a></p> <h4>Next topic</h4> <p class="topless"><a href="bsddb.html" title="next chapter">11.11. <tt class="docutils literal"><span class="pre">bsddb</span></tt> — Interface to Berkeley DB library</a></p> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li><a href="../_sources/library/dbhash.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <form class="search" action="../search.html" method="get"> <input type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="bsddb.html" title="11.11. bsddb — Interface to Berkeley DB library" >next</a> |</li> <li class="right" > <a href="gdbm.html" title="11.9. gdbm — GNU’s reinterpretation of dbm" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="http://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.5 documentation</a> » </li> <li><a href="index.html" >The Python Standard Library</a> »</li> <li><a href="persistence.html" >11. 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