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<li><a class="reference internal" href="#">anydbm – Access to DBM-style databases</a><ul>
<li><a class="reference internal" href="#creating-a-new-database">Creating a New Database</a></li>
<li><a class="reference internal" href="#opening-an-existing-database">Opening an Existing Database</a></li>
<li><a class="reference internal" href="#error-cases">Error Cases</a></li>
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<div class="section" id="module-anydbm">
<span id="anydbm-access-to-dbm-style-databases"></span><h1>anydbm – Access to DBM-style databases<a class="headerlink" href="#module-anydbm" title="Permalink to this headline">¶</a></h1>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Purpose:</th><td class="field-body">anydbm provides a generic dictionary-like interface to DBM-style, string-keyed databases</td>
</tr>
<tr class="field"><th class="field-name">Python Version:</th><td class="field-body">1.4 and later</td>
</tr>
</tbody>
</table>
<p>anydbm is a front-end for DBM-style databases that use simple string
values as keys to access records containing strings. It uses the
<a class="reference internal" href="../whichdb/index.html#module-whichdb" title="whichdb: Identify DBM-style database formats"><tt class="xref py py-mod docutils literal"><span class="pre">whichdb</span></tt></a> module to identify <a class="reference internal" href="../dbhash/index.html#module-dbhash" title="dbhash: DBM-style API for the BSD database library"><tt class="xref py py-mod docutils literal"><span class="pre">dbhash</span></tt></a>, <a class="reference internal" href="../gdbm/index.html#module-gdbm" title="gdbm: GNU's version of the dbm library"><tt class="xref py py-mod docutils literal"><span class="pre">gdbm</span></tt></a>, and
<a class="reference internal" href="../dbm/index.html#module-dbm" title="dbm: Simple database interface"><tt class="xref py py-mod docutils literal"><span class="pre">dbm</span></tt></a> databases, then opens them with the appropriate module. It
is used as a backend for <a class="reference internal" href="../shelve/index.html#module-shelve" title="shelve: Persistent storage of arbitrary Python objects"><tt class="xref py py-mod docutils literal"><span class="pre">shelve</span></tt></a>, which knows how to store
objects using <a class="reference internal" href="../pickle/index.html#module-pickle" title="pickle: Python object serialization"><tt class="xref py py-mod docutils literal"><span class="pre">pickle</span></tt></a>.</p>
<div class="section" id="creating-a-new-database">
<h2>Creating a New Database<a class="headerlink" href="#creating-a-new-database" title="Permalink to this headline">¶</a></h2>
<p>The storage format for new databases is selected by looking for each
of these modules in order:</p>
<ul class="simple">
<li><a class="reference internal" href="../dbhash/index.html#module-dbhash" title="dbhash: DBM-style API for the BSD database library"><tt class="xref py py-mod docutils literal"><span class="pre">dbhash</span></tt></a></li>
<li><a class="reference internal" href="../gdbm/index.html#module-gdbm" title="gdbm: GNU's version of the dbm library"><tt class="xref py py-mod docutils literal"><span class="pre">gdbm</span></tt></a></li>
<li><a class="reference internal" href="../dbm/index.html#module-dbm" title="dbm: Simple database interface"><tt class="xref py py-mod docutils literal"><span class="pre">dbm</span></tt></a></li>
<li><a class="reference internal" href="../dumbdbm/index.html#module-dumbdbm" title="dumbdbm: Portable DBM Implementation"><tt class="xref py py-mod docutils literal"><span class="pre">dumbdbm</span></tt></a></li>
</ul>
<p>The <tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt> function takes <em>flags</em> to control how the database
file is managed. To create a new database when necessary, use
<tt class="docutils literal"><span class="pre">'c'</span></tt>. To always create a new database, use <tt class="docutils literal"><span class="pre">'n'</span></tt>.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">anydbm</span>
<span class="n">db</span> <span class="o">=</span> <span class="n">anydbm</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">'/tmp/example.db'</span><span class="p">,</span> <span class="s">'n'</span><span class="p">)</span>
<span class="n">db</span><span class="p">[</span><span class="s">'key'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'value'</span>
<span class="n">db</span><span class="p">[</span><span class="s">'today'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'Sunday'</span>
<span class="n">db</span><span class="p">[</span><span class="s">'author'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'Doug'</span>
<span class="n">db</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<div class="highlight-python"><pre>$ python anydbm_new.py</pre>
</div>
<p>In this example, the file is always re-initialized. To see what type
of database was created, we can use <a class="reference internal" href="../whichdb/index.html#module-whichdb" title="whichdb: Identify DBM-style database formats"><tt class="xref py py-mod docutils literal"><span class="pre">whichdb</span></tt></a>.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">whichdb</span>
<span class="k">print</span> <span class="n">whichdb</span><span class="o">.</span><span class="n">whichdb</span><span class="p">(</span><span class="s">'/tmp/example.db'</span><span class="p">)</span>
</pre></div>
</div>
<p>Your results may vary, depending on what modules are installed on your
system.</p>
<div class="highlight-python"><pre>$ python anydbm_whichdb.py
dbhash</pre>
</div>
</div>
<div class="section" id="opening-an-existing-database">
<h2>Opening an Existing Database<a class="headerlink" href="#opening-an-existing-database" title="Permalink to this headline">¶</a></h2>
<p>To open an existing database, use <em>flags</em> of either <tt class="docutils literal"><span class="pre">'r'</span></tt> (for
read-only) or <tt class="docutils literal"><span class="pre">'w'</span></tt> (for read-write). You don’t need to worry about
the format, because existing databases are automatically given to
<a class="reference internal" href="../whichdb/index.html#module-whichdb" title="whichdb: Identify DBM-style database formats"><tt class="xref py py-mod docutils literal"><span class="pre">whichdb</span></tt></a> to identify. If a file can be identified, the
appropriate module is used to open it.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">anydbm</span>
<span class="n">db</span> <span class="o">=</span> <span class="n">anydbm</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">'/tmp/example.db'</span><span class="p">,</span> <span class="s">'r'</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="k">print</span> <span class="s">'keys():'</span><span class="p">,</span> <span class="n">db</span><span class="o">.</span><span class="n">keys</span><span class="p">()</span>
<span class="k">for</span> <span class="n">k</span><span class="p">,</span> <span class="n">v</span> <span class="ow">in</span> <span class="n">db</span><span class="o">.</span><span class="n">iteritems</span><span class="p">():</span>
<span class="k">print</span> <span class="s">'iterating:'</span><span class="p">,</span> <span class="n">k</span><span class="p">,</span> <span class="n">v</span>
<span class="k">print</span> <span class="s">'db["author"] ='</span><span class="p">,</span> <span class="n">db</span><span class="p">[</span><span class="s">'author'</span><span class="p">]</span>
<span class="k">finally</span><span class="p">:</span>
<span class="n">db</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>Once open, <tt class="docutils literal"><span class="pre">db</span></tt> is a dictionary-like object, with support for the
usual methods:</p>
<div class="highlight-python"><pre>$ python anydbm_existing.py
keys(): ['author', 'key', 'today']
iterating: author Doug
iterating: key value
iterating: today Sunday
db["author"] = Doug</pre>
</div>
</div>
<div class="section" id="error-cases">
<h2>Error Cases<a class="headerlink" href="#error-cases" title="Permalink to this headline">¶</a></h2>
<p>The keys of the database need to be strings.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">anydbm</span>
<span class="n">db</span> <span class="o">=</span> <span class="n">anydbm</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">'/tmp/example.db'</span><span class="p">,</span> <span class="s">'w'</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">db</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="s">'one'</span>
<span class="k">except</span> <span class="ne">TypeError</span><span class="p">,</span> <span class="n">err</span><span class="p">:</span>
<span class="k">print</span> <span class="s">'</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">err</span><span class="o">.</span><span class="n">__class__</span><span class="o">.</span><span class="n">__name__</span><span class="p">,</span> <span class="n">err</span><span class="p">)</span>
<span class="k">finally</span><span class="p">:</span>
<span class="n">db</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>Passing another type results in a <a class="reference internal" href="../exceptions/index.html#exceptions-typeerror"><em>TypeError</em></a>.</p>
<div class="highlight-python"><pre>$ python anydbm_intkeys.py
TypeError: Integer keys only allowed for Recno and Queue DB's</pre>
</div>
<p>Values must be strings or <tt class="xref docutils literal"><span class="pre">None</span></tt>.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">anydbm</span>
<span class="n">db</span> <span class="o">=</span> <span class="n">anydbm</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">'/tmp/example.db'</span><span class="p">,</span> <span class="s">'w'</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">db</span><span class="p">[</span><span class="s">'one'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">1</span>
<span class="k">except</span> <span class="ne">TypeError</span><span class="p">,</span> <span class="n">err</span><span class="p">:</span>
<span class="k">print</span> <span class="s">'</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">err</span><span class="o">.</span><span class="n">__class__</span><span class="o">.</span><span class="n">__name__</span><span class="p">,</span> <span class="n">err</span><span class="p">)</span>
<span class="k">finally</span><span class="p">:</span>
<span class="n">db</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
</pre></div>
</div>
<p>A similar <a class="reference internal" href="../exceptions/index.html#exceptions-typeerror"><em>TypeError</em></a> is raised if a value
is not a string.</p>
<div class="highlight-python"><pre>$ python anydbm_intvalue.py
TypeError: Data values must be of type string or None.</pre>
</div>
<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="../shelve/index.html#module-shelve" title="shelve: Persistent storage of arbitrary Python objects"><tt class="xref py py-mod docutils literal"><span class="pre">shelve</span></tt></a></dt>
<dd>Examples for the <a class="reference internal" href="../shelve/index.html#module-shelve" title="shelve: Persistent storage of arbitrary Python objects"><tt class="xref py py-mod docutils literal"><span class="pre">shelve</span></tt></a> module, which uses <a class="reference internal" href="#module-anydbm" title="anydbm: anydbm provides a generic dictionary-like interface to DBM-style, string-keyed databases"><tt class="xref py py-mod docutils literal"><span class="pre">anydbm</span></tt></a> to store data.</dd>
<dt><a class="reference external" href="http://docs.python.org/library/anydbm.html">anydbm</a></dt>
<dd>The standard library documentation for this module.</dd>
<dt><a class="reference internal" href="../articles/data_persistence.html#article-data-persistence"><em>Data Persistence and Exchange</em></a></dt>
<dd>Descriptions of other modules for storing data.</dd>
</dl>
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