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<div class="section" id="module-dbhash">
<h1>11.10. <tt class="xref docutils literal"><span class="pre">dbhash</span></tt> — 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 <tt class="xref docutils literal"><span class="pre">dbhash</span></tt> module has been deprecated for removal in Python 3.0.</p>
<p id="index-275">The <tt class="xref docutils literal"><span class="pre">dbhash</span></tt> 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 title="Interface to Berkeley DB database library" class="reference external" href="bsddb.html#module-bsddb"><tt class="xref docutils literal"><span class="pre">bsddb</span></tt></a> module is
required to use <tt class="xref docutils literal"><span class="pre">dbhash</span></tt>.</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>Exception raised on database errors other than <a title="exceptions.KeyError" class="reference external" href="exceptions.html#exceptions.KeyError"><tt class="xref docutils literal"><span class="pre">KeyError</span></tt></a>. It is a synonym
for <tt class="xref docutils literal"><span class="pre">bsddb.error</span></tt>.</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><th class="head">Value</th>
<th class="head">Meaning</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">'r'</span></tt></td>
<td>Open existing database for reading only
(default)</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'w'</span></tt></td>
<td>Open existing database for reading and
writing</td>
</tr>
<tr><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><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 title="Generic interface to DBM-style database modules." class="reference external" href="anydbm.html#module-anydbm"><tt class="xref 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 title="Interface to Berkeley DB database library" class="reference external" href="bsddb.html#module-bsddb"><tt class="xref 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 title="Guess which DBM-style module created a given database." class="reference external" href="whichdb.html#module-whichdb"><tt class="xref 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 title="dbhash.open" class="reference internal" href="#dbhash.open"><tt class="xref 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>It’s possible to loop over every key/value pair in the database using this
method and the <tt class="xref 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.</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>Return the last key/value pair in a database traversal. This may be used to
begin a reverse-order traversal; see <a title="dbhash.dbhash.previous" class="reference internal" href="#dbhash.dbhash.previous"><tt class="xref docutils literal"><span class="pre">previous()</span></tt></a>.</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>Returns the previous key/value pair in a forward-traversal of the database. In
conjunction with <a title="dbhash.dbhash.last" class="reference internal" href="#dbhash.dbhash.last"><tt class="xref docutils literal"><span class="pre">last()</span></tt></a>, this may be used to implement a reverse-order
traversal.</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>This method forces any unwritten data to be written to the disk.</dd></dl>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference external" 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 external" 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 docutils literal"><span class="pre">bsddb</span></tt> — Interface to Berkeley DB library</a></p>
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