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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>11.9. gdbm — GNU’s reinterpretation of dbm — Python 2.7.18 documentation</title> <link rel="stylesheet" href="../_static/classic.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.18 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="11.10. dbhash — DBM-style interface to the BSD database library" href="dbhash.html" /> <link rel="prev" title="11.8. dbm — Simple “database” interface" href="dbm.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/library/gdbm.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"> This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>. You should install the python3 and python3-doc packages and read the <a href="file:///usr/share/doc/python3-doc/html/library/gdbm.html"> Python documentation for the Python3 version packaged in this release</a>. </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="dbhash.html" title="11.10. dbhash — DBM-style interface to the BSD database library" accesskey="N">next</a> |</li> <li class="right" > <a href="dbm.html" title="11.8. dbm — Simple “database” interface" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.18 documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="persistence.html" accesskey="U">11. Data Persistence</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-gdbm"> <span id="gdbm-gnu-s-reinterpretation-of-dbm"></span><h1>11.9. <a class="reference internal" href="#module-gdbm" title="gdbm: GNU's reinterpretation of dbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">gdbm</span></code></a> — GNU’s reinterpretation of dbm<a class="headerlink" href="#module-gdbm" title="Permalink to this headline">¶</a></h1> <div class="admonition note"> <p class="first admonition-title">Note</p> <p class="last">The <a class="reference internal" href="#module-gdbm" title="gdbm: GNU's reinterpretation of dbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">gdbm</span></code></a> module has been renamed to <code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code> in Python 3. The <a class="reference internal" href="../glossary.html#term-2to3"><span class="xref std std-term">2to3</span></a> tool will automatically adapt imports when converting your sources to Python 3.</p> </div> <p id="index-0">This module is quite similar to the <a class="reference internal" href="dbm.html#module-dbm" title="dbm: The standard "database" interface, based on ndbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm</span></code></a> module, but uses <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> instead to provide some additional functionality. Please note that the file formats created by <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> and <code class="docutils literal notranslate"><span class="pre">dbm</span></code> are incompatible.</p> <p>The <a class="reference internal" href="#module-gdbm" title="gdbm: GNU's reinterpretation of dbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">gdbm</span></code></a> module provides an interface to the GNU DBM library. <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> objects behave like mappings (dictionaries), except that keys and values are always strings. Printing a <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> object doesn’t print the keys and values, and the <code class="xref py py-meth docutils literal notranslate"><span class="pre">items()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">values()</span></code> methods are not supported.</p> <p>The module defines the following constant and functions:</p> <dl class="exception"> <dt id="gdbm.error"> <em class="property">exception </em><code class="descclassname">gdbm.</code><code class="descname">error</code><a class="headerlink" href="#gdbm.error" title="Permalink to this definition">¶</a></dt> <dd><p>Raised on <code class="docutils literal notranslate"><span class="pre">gdbm</span></code>-specific errors, such as I/O errors. <a class="reference internal" href="exceptions.html#exceptions.KeyError" title="exceptions.KeyError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyError</span></code></a> is raised for general mapping errors like specifying an incorrect key.</p> </dd></dl> <dl class="function"> <dt id="gdbm.open"> <code class="descclassname">gdbm.</code><code class="descname">open</code><span class="sig-paren">(</span><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><span class="sig-paren">)</span><a class="headerlink" href="#gdbm.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open a <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> database and return a <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> 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 class="row-odd"><th class="head">Value</th> <th class="head">Meaning</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'r'</span></code></td> <td>Open existing database for reading only (default)</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'w'</span></code></td> <td>Open existing database for reading and writing</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'c'</span></code></td> <td>Open database for reading and writing, creating it if it doesn’t exist</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'n'</span></code></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 class="row-odd"><th class="head">Value</th> <th class="head">Meaning</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'f'</span></code></td> <td>Open the database in fast mode. Writes to the database will not be synchronized.</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">'s'</span></code></td> <td>Synchronized mode. This will cause changes to the database to be immediately written to the file.</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">'u'</span></code></td> <td>Do not lock database.</td> </tr> </tbody> </table> <p>Not all flags are valid for all versions of <code class="docutils literal notranslate"><span class="pre">gdbm</span></code>. The module constant <code class="xref py py-const docutils literal notranslate"><span class="pre">open_flags</span></code> is a string of supported flag characters. The exception <a class="reference internal" href="#gdbm.error" title="gdbm.error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">error</span></code></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 <code class="docutils literal notranslate"><span class="pre">0666</span></code>.</p> </dd></dl> <p>In addition to the dictionary-like methods, <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> objects have the following methods:</p> <dl class="function"> <dt id="gdbm.firstkey"> <code class="descclassname">gdbm.</code><code class="descname">firstkey</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#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="#gdbm.nextkey" title="gdbm.nextkey"><code class="xref py py-meth docutils literal notranslate"><span class="pre">nextkey()</span></code></a> method. The traversal is ordered by <code class="docutils literal notranslate"><span class="pre">gdbm</span></code>’s internal hash values, and won’t be sorted by the key values. This method returns the starting key.</p> </dd></dl> <dl class="function"> <dt id="gdbm.nextkey"> <code class="descclassname">gdbm.</code><code class="descname">nextkey</code><span class="sig-paren">(</span><em>key</em><span class="sig-paren">)</span><a class="headerlink" href="#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 <code class="docutils literal notranslate"><span class="pre">db</span></code>, without having to create a list in memory that contains them all:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><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="kc">None</span><span class="p">:</span> <span class="nb">print</span> <span class="n">k</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="function"> <dt id="gdbm.reorganize"> <code class="descclassname">gdbm.</code><code class="descname">reorganize</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#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 <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> file, this routine will reorganize the database. <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> 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="function"> <dt id="gdbm.sync"> <code class="descclassname">gdbm.</code><code class="descname">sync</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#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> <dl class="function"> <dt id="gdbm.close"> <code class="descclassname">gdbm.</code><code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#gdbm.close" title="Permalink to this definition">¶</a></dt> <dd><p>Close the <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> database.</p> </dd></dl> <div class="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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">anydbm</span></code></a></dt> <dd>Generic interface to <code class="docutils literal notranslate"><span class="pre">dbm</span></code>-style databases.</dd> <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 notranslate"><span class="pre">whichdb</span></code></a></dt> <dd>Utility module used to determine the type of an existing database.</dd> </dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h4>Previous topic</h4> <p class="topless"><a href="dbm.html" title="previous chapter">11.8. <code class="docutils literal notranslate"><span class="pre">dbm</span></code> — Simple “database” interface</a></p> <h4>Next topic</h4> <p class="topless"><a href="dbhash.html" title="next chapter">11.10. <code class="docutils literal notranslate"><span class="pre">dbhash</span></code> — DBM-style interface to the BSD database library</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/library/gdbm.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3>Quick search</h3> <div class="searchformwrapper"> <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> </div> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <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="dbhash.html" title="11.10. dbhash — DBM-style interface to the BSD database library" >next</a> |</li> <li class="right" > <a href="dbm.html" title="11.8. dbm — Simple “database” interface" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; 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