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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-dbm"> <span id="dbm-interfaces-to-unix-databases"></span><h1>12.5. <a class="reference internal" href="#module-dbm" title="dbm: Interfaces to various Unix "database" formats."><tt class="xref py py-mod docutils literal"><span class="pre">dbm</span></tt></a> — Interfaces to Unix “databases”<a class="headerlink" href="#module-dbm" title="Permalink to this headline">¶</a></h1> <p><a class="reference internal" href="#module-dbm" title="dbm: Interfaces to various Unix "database" formats."><tt class="xref py py-mod docutils literal"><span class="pre">dbm</span></tt></a> is a generic interface to variants of the DBM database — <a class="reference internal" href="#module-dbm.gnu" title="dbm.gnu: GNU's reinterpretation of dbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.gnu</span></tt></a> or <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.ndbm</span></tt></a>. If none of these modules is installed, the slow-but-simple implementation in module <a class="reference internal" href="#module-dbm.dumb" title="dbm.dumb: Portable implementation of the simple DBM interface."><tt class="xref py py-mod docutils literal"><span class="pre">dbm.dumb</span></tt></a> will be used. There is a <a class="reference external" href="http://www.jcea.es/programacion/pybsddb.htm">third party interface</a> to the Oracle Berkeley DB.</p> <dl class="exception"> <dt id="dbm.error"> <em class="property">exception </em><tt class="descclassname">dbm.</tt><tt class="descname">error</tt><a class="headerlink" href="#dbm.error" title="Permalink to this definition">¶</a></dt> <dd><p>A tuple containing the exceptions that can be raised by each of the supported modules, with a unique exception also named <a class="reference internal" href="#dbm.error" title="dbm.error"><tt class="xref py py-exc docutils literal"><span class="pre">dbm.error</span></tt></a> as the first item — the latter is used when <a class="reference internal" href="#dbm.error" title="dbm.error"><tt class="xref py py-exc docutils literal"><span class="pre">dbm.error</span></tt></a> is raised.</p> </dd></dl> <dl class="function"> <dt id="dbm.whichdb"> <tt class="descclassname">dbm.</tt><tt class="descname">whichdb</tt><big>(</big><em>filename</em><big>)</big><a class="headerlink" href="#dbm.whichdb" title="Permalink to this definition">¶</a></dt> <dd><p>This function attempts to guess which of the several simple database modules available — <a class="reference internal" href="#module-dbm.gnu" title="dbm.gnu: GNU's reinterpretation of dbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.gnu</span></tt></a>, <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.ndbm</span></tt></a> or <a class="reference internal" href="#module-dbm.dumb" title="dbm.dumb: Portable implementation of the simple DBM interface."><tt class="xref py py-mod docutils literal"><span class="pre">dbm.dumb</span></tt></a> — should be used to open a given file.</p> <p>Returns one of the following values: <tt class="xref docutils literal"><span class="pre">None</span></tt> if the file can’t be opened because it’s unreadable or doesn’t exist; the empty string (<tt class="docutils literal"><span class="pre">''</span></tt>) if the file’s format can’t be guessed; or a string containing the required module name, such as <tt class="docutils literal"><span class="pre">'dbm.ndbm'</span></tt> or <tt class="docutils literal"><span class="pre">'dbm.gnu'</span></tt>.</p> </dd></dl> <dl class="function"> <dt id="dbm.open"> <tt class="descclassname">dbm.</tt><tt class="descname">open</tt><big>(</big><em>file</em>, <em>flag='r'</em>, <em>mode=0o666</em><big>)</big><a class="headerlink" href="#dbm.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open the database file <em>file</em> and return a corresponding object.</p> <p>If the database file already exists, the <a class="reference internal" href="#dbm.whichdb" title="dbm.whichdb"><tt class="xref py py-func docutils literal"><span class="pre">whichdb()</span></tt></a> function is used to determine its type and the appropriate module is used; if it does not exist, the first module listed above that can be imported is used.</p> <p>The optional <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>The optional <em>mode</em> argument is the Unix mode of the file, used only when the database has to be created. It defaults to octal <tt class="docutils literal"><span class="pre">0o666</span></tt> (and will be modified by the prevailing umask).</p> </dd></dl> <p>The object returned by <a class="reference internal" href="#dbm.open" title="dbm.open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> supports the same basic functionality as dictionaries; keys and their corresponding values can be stored, retrieved, and deleted, and the <a class="reference internal" href="../reference/expressions.html#in"><tt class="xref std std-keyword docutils literal"><span class="pre">in</span></tt></a> operator and the <tt class="xref py py-meth docutils literal"><span class="pre">keys()</span></tt> method are available, as well as <tt class="xref py py-meth docutils literal"><span class="pre">get()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">setdefault()</span></tt>.</p> <p class="versionchanged"> <span class="versionmodified">Changed in version 3.2:</span> <tt class="xref py py-meth docutils literal"><span class="pre">get()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">setdefault()</span></tt> are now available in all database modules.</p> <p>Key and values are always stored as bytes. This means that when strings are used they are implicitly converted to the default encoding before being stored.</p> <p>The following example records some hostnames and a corresponding title, and then prints out the contents of the database:</p> <div class="highlight-python3"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">dbm</span> <span class="c"># Open database, creating it if necessary.</span> <span class="n">db</span> <span class="o">=</span> <span class="n">dbm</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s">'cache'</span><span class="p">,</span> <span class="s">'c'</span><span class="p">)</span> <span class="c"># Record some values</span> <span class="n">db</span><span class="p">[</span><span class="n">b</span><span class="s">'hello'</span><span class="p">]</span> <span class="o">=</span> <span class="n">b</span><span class="s">'there'</span> <span class="n">db</span><span class="p">[</span><span class="s">'www.python.org'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'Python Website'</span> <span class="n">db</span><span class="p">[</span><span class="s">'www.cnn.com'</span><span class="p">]</span> <span class="o">=</span> <span class="s">'Cable News Network'</span> <span class="c"># Note that the keys are considered bytes now.</span> <span class="k">assert</span> <span class="n">db</span><span class="p">[</span><span class="n">b</span><span class="s">'www.python.org'</span><span class="p">]</span> <span class="o">==</span> <span class="n">b</span><span class="s">'Python Website'</span> <span class="c"># Notice how the value is now in bytes.</span> <span class="k">assert</span> <span class="n">db</span><span class="p">[</span><span class="s">'www.cnn.com'</span><span class="p">]</span> <span class="o">==</span> <span class="n">b</span><span class="s">'Cable News Network'</span> <span class="c"># Often-used methods of the dict interface work too.</span> <span class="nb">print</span><span class="p">(</span><span class="n">db</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'python.org'</span><span class="p">,</span> <span class="n">b</span><span class="s">'not present'</span><span class="p">))</span> <span class="c"># Storing a non-string key or value will raise an exception (most</span> <span class="c"># likely a TypeError).</span> <span class="n">db</span><span class="p">[</span><span class="s">'www.yahoo.com'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">4</span> <span class="c"># Close when done.</span> <span class="n">db</span><span class="o">.</span><span class="n">close</span><span class="p">()</span> </pre></div> </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.html#module-shelve" title="shelve: Python object persistence."><tt class="xref py py-mod docutils literal"><span class="pre">shelve</span></tt></a></dt> <dd>Persistence module which stores non-string data.</dd> </dl> </div> <p>The individual submodules are described in the following sections.</p> <div class="section" id="module-dbm.gnu"> <span id="dbm-gnu-gnu-s-reinterpretation-of-dbm"></span><h2>12.5.1. <a class="reference internal" href="#module-dbm.gnu" title="dbm.gnu: GNU's reinterpretation of dbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.gnu</span></tt></a> — GNU’s reinterpretation of dbm<a class="headerlink" href="#module-dbm.gnu" title="Permalink to this headline">¶</a></h2> <p><em>Platforms: </em>Unix</p> <p>This module is quite similar to the <a class="reference internal" href="#module-dbm" title="dbm: Interfaces to various Unix "database" formats."><tt class="xref py py-mod docutils literal"><span class="pre">dbm</span></tt></a> module, but uses the GNU library <tt class="docutils literal"><span class="pre">gdbm</span></tt> instead to provide some additional functionality. Please note that the file formats created by <a class="reference internal" href="#module-dbm.gnu" title="dbm.gnu: GNU's reinterpretation of dbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.gnu</span></tt></a> and <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.ndbm</span></tt></a> are incompatible.</p> <p>The <a class="reference internal" href="#module-dbm.gnu" title="dbm.gnu: GNU's reinterpretation of dbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.gnu</span></tt></a> module provides an interface to the GNU DBM library. <tt class="docutils literal"><span class="pre">dbm.gnu.gdbm</span></tt> objects behave like mappings (dictionaries), except that keys and values are always converted to bytes before storing. Printing a <tt class="docutils literal"><span class="pre">gdbm</span></tt> object doesn’t print the keys and values, and the <tt class="xref py py-meth docutils literal"><span class="pre">items()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">values()</span></tt> methods are not supported.</p> <dl class="exception"> <dt id="dbm.gnu.error"> <em class="property">exception </em><tt class="descclassname">dbm.gnu.</tt><tt class="descname">error</tt><a class="headerlink" href="#dbm.gnu.error" title="Permalink to this definition">¶</a></dt> <dd><p>Raised on <a class="reference internal" href="#module-dbm.gnu" title="dbm.gnu: GNU's reinterpretation of dbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.gnu</span></tt></a>-specific errors, such as I/O errors. <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><tt class="xref py py-exc docutils literal"><span class="pre">KeyError</span></tt></a> is raised for general mapping errors like specifying an incorrect key.</p> </dd></dl> <dl class="function"> <dt id="dbm.gnu.open"> <tt class="descclassname">dbm.gnu.</tt><tt class="descname">open</tt><big>(</big><em>filename</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="#dbm.gnu.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open a <tt class="docutils literal"><span class="pre">gdbm</span></tt> database and return a <tt class="xref py py-class docutils literal"><span class="pre">gdbm</span></tt> object. The <em>filename</em> argument is the name of the database file.</p> <p>The optional <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>The following additional characters may be appended to the flag to control how the database is opened:</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">'f'</span></tt></td> <td>Open the database in fast mode. Writes to the database will not be synchronized.</td> </tr> <tr><td><tt class="docutils literal"><span class="pre">'s'</span></tt></td> <td>Synchronized mode. This will cause changes to the database to be immediately written to the file.</td> </tr> <tr><td><tt class="docutils literal"><span class="pre">'u'</span></tt></td> <td>Do not lock database.</td> </tr> </tbody> </table> <p>Not all flags are valid for all versions of <tt class="docutils literal"><span class="pre">gdbm</span></tt>. The module constant <tt class="xref py py-const docutils literal"><span class="pre">open_flags</span></tt> is a string of supported flag characters. The exception <a class="reference internal" href="#dbm.gnu.error" title="dbm.gnu.error"><tt class="xref py py-exc docutils literal"><span class="pre">error</span></tt></a> is raised if an invalid flag is specified.</p> <p>The optional <em>mode</em> argument is the Unix mode of the file, used only when the database has to be created. It defaults to octal <tt class="docutils literal"><span class="pre">0o666</span></tt>.</p> <p>In addition to the dictionary-like methods, <tt class="docutils literal"><span class="pre">gdbm</span></tt> objects have the following methods:</p> <dl class="method"> <dt id="dbm.gnu.gdbm.firstkey"> <tt class="descclassname">gdbm.</tt><tt class="descname">firstkey</tt><big>(</big><big>)</big><a class="headerlink" href="#dbm.gnu.gdbm.firstkey" title="Permalink to this definition">¶</a></dt> <dd><p>It’s possible to loop over every key in the database using this method and the <a class="reference internal" href="#dbm.gnu.gdbm.nextkey" title="dbm.gnu.gdbm.nextkey"><tt class="xref py py-meth docutils literal"><span class="pre">nextkey()</span></tt></a> method. The traversal is ordered by <tt class="docutils literal"><span class="pre">gdbm</span></tt>‘s 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="dbm.gnu.gdbm.nextkey"> <tt class="descclassname">gdbm.</tt><tt class="descname">nextkey</tt><big>(</big><em>key</em><big>)</big><a class="headerlink" href="#dbm.gnu.gdbm.nextkey" title="Permalink to this definition">¶</a></dt> <dd><p>Returns the key that follows <em>key</em> in the 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-python3"><div class="highlight"><pre><span class="n">k</span> <span class="o">=</span> <span class="n">db</span><span class="o">.</span><span class="n">firstkey</span><span class="p">()</span> <span class="k">while</span> <span class="n">k</span> <span class="o">!=</span> <span class="k">None</span><span class="p">:</span> <span class="nb">print</span><span class="p">(</span><span class="n">k</span><span class="p">)</span> <span class="n">k</span> <span class="o">=</span> <span class="n">db</span><span class="o">.</span><span class="n">nextkey</span><span class="p">(</span><span class="n">k</span><span class="p">)</span> </pre></div> </div> </dd></dl> <dl class="method"> <dt id="dbm.gnu.gdbm.reorganize"> <tt class="descclassname">gdbm.</tt><tt class="descname">reorganize</tt><big>(</big><big>)</big><a class="headerlink" href="#dbm.gnu.gdbm.reorganize" title="Permalink to this definition">¶</a></dt> <dd><p>If you have carried out a lot of deletions and would like to shrink the space used by the <tt class="docutils literal"><span class="pre">gdbm</span></tt> file, this routine will reorganize the database. <tt class="docutils literal"><span class="pre">gdbm</span></tt> objects will not shorten the length of a database file except by using this reorganization; otherwise, deleted file space will be kept and reused as new (key, value) pairs are added.</p> </dd></dl> <dl class="method"> <dt id="dbm.gnu.gdbm.sync"> <tt class="descclassname">gdbm.</tt><tt class="descname">sync</tt><big>(</big><big>)</big><a class="headerlink" href="#dbm.gnu.gdbm.sync" title="Permalink to this definition">¶</a></dt> <dd><p>When the database has been opened in fast mode, this method forces any unwritten data to be written to the disk.</p> </dd></dl> </dd></dl> </div> <div class="section" id="module-dbm.ndbm"> <span id="dbm-ndbm-interface-based-on-ndbm"></span><h2>12.5.2. <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.ndbm</span></tt></a> — Interface based on ndbm<a class="headerlink" href="#module-dbm.ndbm" title="Permalink to this headline">¶</a></h2> <p><em>Platforms: </em>Unix</p> <p>The <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.ndbm</span></tt></a> module provides an interface to the Unix “(n)dbm” library. Dbm objects behave like mappings (dictionaries), except that keys and values are always stored as bytes. Printing a <tt class="docutils literal"><span class="pre">dbm</span></tt> object doesn’t print the keys and values, and the <tt class="xref py py-meth docutils literal"><span class="pre">items()</span></tt> and <tt class="xref py py-meth docutils literal"><span class="pre">values()</span></tt> methods are not supported.</p> <p>This module can be used with the “classic” ndbm interface or the GNU GDBM compatibility interface. On Unix, the <strong class="program">configure</strong> script will attempt to locate the appropriate header file to simplify building this module.</p> <dl class="exception"> <dt id="dbm.ndbm.error"> <em class="property">exception </em><tt class="descclassname">dbm.ndbm.</tt><tt class="descname">error</tt><a class="headerlink" href="#dbm.ndbm.error" title="Permalink to this definition">¶</a></dt> <dd><p>Raised on <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.ndbm</span></tt></a>-specific errors, such as I/O errors. <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><tt class="xref py py-exc docutils literal"><span class="pre">KeyError</span></tt></a> is raised for general mapping errors like specifying an incorrect key.</p> </dd></dl> <dl class="data"> <dt id="dbm.ndbm.library"> <tt class="descclassname">dbm.ndbm.</tt><tt class="descname">library</tt><a class="headerlink" href="#dbm.ndbm.library" title="Permalink to this definition">¶</a></dt> <dd><p>Name of the <tt class="docutils literal"><span class="pre">ndbm</span></tt> implementation library used.</p> </dd></dl> <dl class="function"> <dt id="dbm.ndbm.open"> <tt class="descclassname">dbm.ndbm.</tt><tt class="descname">open</tt><big>(</big><em>filename</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="#dbm.ndbm.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open a dbm database and return a <tt class="docutils literal"><span class="pre">dbm</span></tt> object. The <em>filename</em> argument is the name of the database file (without the <tt class="file docutils literal"><span class="pre">.dir</span></tt> or <tt class="file docutils literal"><span class="pre">.pag</span></tt> extensions).</p> <p>The optional <em>flag</em> argument must be one of these values:</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>The optional <em>mode</em> argument is the Unix mode of the file, used only when the database has to be created. It defaults to octal <tt class="docutils literal"><span class="pre">0o666</span></tt> (and will be modified by the prevailing umask).</p> </dd></dl> </div> <div class="section" id="module-dbm.dumb"> <span id="dbm-dumb-portable-dbm-implementation"></span><h2>12.5.3. <a class="reference internal" href="#module-dbm.dumb" title="dbm.dumb: Portable implementation of the simple DBM interface."><tt class="xref py py-mod docutils literal"><span class="pre">dbm.dumb</span></tt></a> — Portable DBM implementation<a class="headerlink" href="#module-dbm.dumb" title="Permalink to this headline">¶</a></h2> <div class="admonition note" id="index-0"> <p class="first admonition-title">Note</p> <p class="last">The <a class="reference internal" href="#module-dbm.dumb" title="dbm.dumb: Portable implementation of the simple DBM interface."><tt class="xref py py-mod docutils literal"><span class="pre">dbm.dumb</span></tt></a> module is intended as a last resort fallback for the <a class="reference internal" href="#module-dbm" title="dbm: Interfaces to various Unix "database" formats."><tt class="xref py py-mod docutils literal"><span class="pre">dbm</span></tt></a> module when a more robust module is not available. The <a class="reference internal" href="#module-dbm.dumb" title="dbm.dumb: Portable implementation of the simple DBM interface."><tt class="xref py py-mod docutils literal"><span class="pre">dbm.dumb</span></tt></a> module is not written for speed and is not nearly as heavily used as the other database modules.</p> </div> <p>The <a class="reference internal" href="#module-dbm.dumb" title="dbm.dumb: Portable implementation of the simple DBM interface."><tt class="xref py py-mod docutils literal"><span class="pre">dbm.dumb</span></tt></a> module provides a persistent dictionary-like interface which is written entirely in Python. Unlike other modules such as <a class="reference internal" href="#module-dbm.gnu" title="dbm.gnu: GNU's reinterpretation of dbm. (Unix)"><tt class="xref py py-mod docutils literal"><span class="pre">dbm.gnu</span></tt></a> no external library is required. As with other persistent mappings, the keys and values are always stored as bytes.</p> <p>The module defines the following:</p> <dl class="exception"> <dt id="dbm.dumb.error"> <em class="property">exception </em><tt class="descclassname">dbm.dumb.</tt><tt class="descname">error</tt><a class="headerlink" href="#dbm.dumb.error" title="Permalink to this definition">¶</a></dt> <dd><p>Raised on <a class="reference internal" href="#module-dbm.dumb" title="dbm.dumb: Portable implementation of the simple DBM interface."><tt class="xref py py-mod docutils literal"><span class="pre">dbm.dumb</span></tt></a>-specific errors, such as I/O errors. <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><tt class="xref py py-exc docutils literal"><span class="pre">KeyError</span></tt></a> is raised for general mapping errors like specifying an incorrect key.</p> </dd></dl> <dl class="function"> <dt id="dbm.dumb.open"> <tt class="descclassname">dbm.dumb.</tt><tt class="descname">open</tt><big>(</big><em>filename</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="#dbm.dumb.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open a <tt class="docutils literal"><span class="pre">dumbdbm</span></tt> database and return a dumbdbm object. The <em>filename</em> argument is the basename of the database file (without any specific extensions). When a dumbdbm database is created, files with <tt class="file docutils literal"><span class="pre">.dat</span></tt> and <tt class="file docutils literal"><span class="pre">.dir</span></tt> extensions are created.</p> <p>The optional <em>flag</em> argument is currently ignored; the database is always opened for update, and will be created if it does not exist.</p> <p>The optional <em>mode</em> argument is the Unix mode of the file, used only when the database has to be created. It defaults to octal <tt class="docutils literal"><span class="pre">0o666</span></tt> (and will be modified by the prevailing umask).</p> <p>In addition to the methods provided by the <tt class="xref py py-class docutils literal"><span class="pre">collections.MutableMapping</span></tt> class, <tt class="xref py py-class docutils literal"><span class="pre">dumbdbm</span></tt> objects provide the following method:</p> <dl class="method"> <dt id="dbm.dumb.dumbdbm.sync"> <tt class="descclassname">dumbdbm.</tt><tt class="descname">sync</tt><big>(</big><big>)</big><a class="headerlink" href="#dbm.dumb.dumbdbm.sync" title="Permalink to this definition">¶</a></dt> <dd><p>Synchronize the on-disk directory and data files. This method is called by the <tt class="xref py py-meth docutils literal"><span class="pre">Shelve.sync()</span></tt> method.</p> </dd></dl> </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="#">12.5. <tt class="docutils literal"><span class="pre">dbm</span></tt> — Interfaces to Unix “databases”</a><ul> <li><a class="reference internal" href="#module-dbm.gnu">12.5.1. <tt class="docutils literal"><span class="pre">dbm.gnu</span></tt> — GNU’s reinterpretation of dbm</a></li> <li><a class="reference internal" href="#module-dbm.ndbm">12.5.2. <tt class="docutils literal"><span class="pre">dbm.ndbm</span></tt> — Interface based on ndbm</a></li> <li><a class="reference internal" href="#module-dbm.dumb">12.5.3. <tt class="docutils literal"><span class="pre">dbm.dumb</span></tt> — Portable DBM implementation</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="marshal.html" title="previous chapter">12.4. <tt class="docutils literal"><span class="pre">marshal</span></tt> — Internal Python object serialization</a></p> <h4>Next topic</h4> <p class="topless"><a href="sqlite3.html" title="next chapter">12.6. <tt class="docutils literal docutils literal"><span class="pre">sqlite3</span></tt> — DB-API 2.0 interface for SQLite databases</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/dbm.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" size="18" /> <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="sqlite3.html" title="12.6. sqlite3 — DB-API 2.0 interface for SQLite databases" >next</a> |</li> <li class="right" > <a href="marshal.html" title="12.4. marshal — Internal Python object serialization" >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">3.3.2 Documentation</a> » </li> <li><a href="index.html" >The Python Standard Library</a> »</li> <li><a href="persistence.html" >12. Data Persistence</a> »</li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 1990-2013, Python Software Foundation. <br /> The Python Software Foundation is a non-profit corporation. <a href="http://www.python.org/psf/donations/">Please donate.</a> <br /> Last updated on May 15, 2013. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.0.7. </div> </body> </html>