<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="utf-8" />
<title>11.9. gdbm — GNU’s reinterpretation of dbm — Python 2.7.17 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 2.7.17 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="https://docs.python.org/2/library/gdbm.html" />
<script type="text/javascript" src="../_static/copybutton.js"></script>
</head><body>
<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 2.7.17 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="admonition-title">Note</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 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 class="docutils align-center">
<colgroup>
<col style="width: 17%" />
<col style="width: 83%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Value</p></th>
<th class="head"><p>Meaning</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'r'</span></code></p></td>
<td><p>Open existing database for reading only
(default)</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'w'</span></code></p></td>
<td><p>Open existing database for reading and
writing</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'c'</span></code></p></td>
<td><p>Open database for reading and writing,
creating it if it doesn’t exist</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'n'</span></code></p></td>
<td><p>Always create a new, empty database, open
for reading and writing</p></td>
</tr>
</tbody>
</table>
<p>The following additional characters may be appended to the flag to control
how the database is opened:</p>
<table class="docutils align-center">
<colgroup>
<col style="width: 17%" />
<col style="width: 83%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Value</p></th>
<th class="head"><p>Meaning</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'f'</span></code></p></td>
<td><p>Open the database in fast mode. Writes
to the database will not be synchronized.</p></td>
</tr>
<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'s'</span></code></p></td>
<td><p>Synchronized mode. This will cause changes
to the database to be immediately written
to the file.</p></td>
</tr>
<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'u'</span></code></p></td>
<td><p>Do not lock database.</p></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="admonition-title">See also</p>
<dl class="simple">
<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><p>Generic interface to <code class="docutils literal notranslate"><span class="pre">dbm</span></code>-style databases.</p>
</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><p>Utility module used to determine the type of an existing database.</p>
</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="xref py py-mod 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="xref py py-mod 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" />
</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; margin-top: -1px"/></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li>
<a href="../index.html">Python 2.7.17 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" >11. Data Persistence</a> »</li>
</ul>
</div>
<div class="footer">
© <a href="../copyright.html">Copyright</a> 1990-2019, Python Software Foundation.
<br />
The Python Software Foundation is a non-profit corporation.
<a href="https://www.python.org/psf/donations/">Please donate.</a>
<br />
Last updated on Oct 19, 2019.
<a href="../bugs.html">Found a bug</a>?
<br />
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 2.0.1.
</div>
</body>
</html>
distrib
>
Mageia
>
7
>
armv7hl
>
media
>
core-updates
>
by-pkgid
>
e1011ddec34cda34f3a002b121247943
>
files
>
786
