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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>12.5. dbm — Interfaces to Unix “databases” — Python 3.6.7 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.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/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.6.7 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="12.6. sqlite3 — DB-API 2.0 interface for SQLite databases" href="sqlite3.html" /> <link rel="prev" title="12.4. marshal — Internal Python object serialization" href="marshal.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/library/dbm.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="sqlite3.html" title="12.6. sqlite3 — DB-API 2.0 interface for SQLite databases" accesskey="N">next</a> |</li> <li class="right" > <a href="marshal.html" title="12.4. marshal — Internal Python object serialization" 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">3.6.7 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">12. Data Persistence</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" 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> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm</span></code></a> — Interfaces to Unix “databases”<a class="headerlink" href="#module-dbm" title="Permalink to this headline">¶</a></h1> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/dbm/__init__.py">Lib/dbm/__init__.py</a></p> <hr class="docutils" /> <p><a class="reference internal" href="#module-dbm" title="dbm: Interfaces to various Unix "database" formats."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm</span></code></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)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code></a> or <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.ndbm</span></code></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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.dumb</span></code></a> will be used. There is a <a class="reference external" href="https://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><code class="descclassname">dbm.</code><code class="descname">error</code><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"><code class="xref py py-exc docutils literal notranslate"><span class="pre">dbm.error</span></code></a> as the first item — the latter is used when <a class="reference internal" href="#dbm.error" title="dbm.error"><code class="xref py py-exc docutils literal notranslate"><span class="pre">dbm.error</span></code></a> is raised.</p> </dd></dl> <dl class="function"> <dt id="dbm.whichdb"> <code class="descclassname">dbm.</code><code class="descname">whichdb</code><span class="sig-paren">(</span><em>filename</em><span class="sig-paren">)</span><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)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code></a>, <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.ndbm</span></code></a> or <a class="reference internal" href="#module-dbm.dumb" title="dbm.dumb: Portable implementation of the simple DBM interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.dumb</span></code></a> — should be used to open a given file.</p> <p>Returns one of the following values: <code class="docutils literal notranslate"><span class="pre">None</span></code> if the file can’t be opened because it’s unreadable or doesn’t exist; the empty string (<code class="docutils literal notranslate"><span class="pre">''</span></code>) if the file’s format can’t be guessed; or a string containing the required module name, such as <code class="docutils literal notranslate"><span class="pre">'dbm.ndbm'</span></code> or <code class="docutils literal notranslate"><span class="pre">'dbm.gnu'</span></code>.</p> </dd></dl> <dl class="function"> <dt id="dbm.open"> <code class="descclassname">dbm.</code><code class="descname">open</code><span class="sig-paren">(</span><em>file</em>, <em>flag='r'</em>, <em>mode=0o666</em><span class="sig-paren">)</span><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"><code class="xref py py-func docutils literal notranslate"><span class="pre">whichdb()</span></code></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 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 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">0o666</span></code> (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"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></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"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">in</span></code></a> operator and the <code class="xref py py-meth docutils literal notranslate"><span class="pre">keys()</span></code> method are available, as well as <code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">setdefault()</span></code>.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.2: </span><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">setdefault()</span></code> are now available in all database modules.</p> </div> <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>These objects also support being used in a <a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code></a> statement, which will automatically close them when done.</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.4: </span>Added native support for the context management protocol to the objects returned by <a class="reference internal" href="#dbm.open" title="dbm.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a>.</p> </div> <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 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">dbm</span> <span class="c1"># Open database, creating it if necessary.</span> <span class="k">with</span> <span class="n">dbm</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s1">'cache'</span><span class="p">,</span> <span class="s1">'c'</span><span class="p">)</span> <span class="k">as</span> <span class="n">db</span><span class="p">:</span> <span class="c1"># Record some values</span> <span class="n">db</span><span class="p">[</span><span class="sa">b</span><span class="s1">'hello'</span><span class="p">]</span> <span class="o">=</span> <span class="sa">b</span><span class="s1">'there'</span> <span class="n">db</span><span class="p">[</span><span class="s1">'www.python.org'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'Python Website'</span> <span class="n">db</span><span class="p">[</span><span class="s1">'www.cnn.com'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'Cable News Network'</span> <span class="c1"># 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="sa">b</span><span class="s1">'www.python.org'</span><span class="p">]</span> <span class="o">==</span> <span class="sa">b</span><span class="s1">'Python Website'</span> <span class="c1"># 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="s1">'www.cnn.com'</span><span class="p">]</span> <span class="o">==</span> <span class="sa">b</span><span class="s1">'Cable News Network'</span> <span class="c1"># 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="s1">'python.org'</span><span class="p">,</span> <span class="sa">b</span><span class="s1">'not present'</span><span class="p">))</span> <span class="c1"># Storing a non-string key or value will raise an exception (most</span> <span class="c1"># likely a TypeError).</span> <span class="n">db</span><span class="p">[</span><span class="s1">'www.yahoo.com'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">4</span> <span class="c1"># db is automatically closed when leaving the with statement.</span> </pre></div> </div> <div class="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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code></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)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code></a> — GNU’s reinterpretation of dbm<a class="headerlink" href="#module-dbm.gnu" title="Permalink to this headline">¶</a></h2> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/dbm/gnu.py">Lib/dbm/gnu.py</a></p> <hr class="docutils" /> <p>This module is quite similar to the <a class="reference internal" href="#module-dbm" title="dbm: Interfaces to various Unix "database" formats."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm</span></code></a> module, but uses the GNU library <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 <a class="reference internal" href="#module-dbm.gnu" title="dbm.gnu: GNU's reinterpretation of dbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code></a> and <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.ndbm</span></code></a> are incompatible.</p> <p>The <a class="reference internal" href="#module-dbm.gnu" title="dbm.gnu: GNU's reinterpretation of dbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code></a> module provides an interface to the GNU DBM library. <code class="docutils literal notranslate"><span class="pre">dbm.gnu.gdbm</span></code> objects behave like mappings (dictionaries), except that keys and values are always converted to bytes before storing. 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> <dl class="exception"> <dt id="dbm.gnu.error"> <em class="property">exception </em><code class="descclassname">dbm.gnu.</code><code class="descname">error</code><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)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code></a>-specific errors, such as I/O errors. <a class="reference internal" href="exceptions.html#KeyError" title="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="dbm.gnu.open"> <code class="descclassname">dbm.gnu.</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="#dbm.gnu.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="xref py py-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="#dbm.gnu.error" title="dbm.gnu.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">0o666</span></code>.</p> <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="method"> <dt id="dbm.gnu.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="#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"><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="method"> <dt id="dbm.gnu.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="#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 <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-python3 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="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"> <code class="descclassname">gdbm.</code><code class="descname">reorganize</code><span class="sig-paren">(</span><span class="sig-paren">)</span><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 <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> 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"> <code class="descclassname">gdbm.</code><code class="descname">sync</code><span class="sig-paren">(</span><span class="sig-paren">)</span><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> <dl class="method"> <dt id="dbm.gnu.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="#dbm.gnu.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> </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)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.ndbm</span></code></a> — Interface based on ndbm<a class="headerlink" href="#module-dbm.ndbm" title="Permalink to this headline">¶</a></h2> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/dbm/ndbm.py">Lib/dbm/ndbm.py</a></p> <hr class="docutils" /> <p>The <a class="reference internal" href="#module-dbm.ndbm" title="dbm.ndbm: The standard "database" interface, based on ndbm. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.ndbm</span></code></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 <code class="docutils literal notranslate"><span class="pre">dbm</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>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><code class="descclassname">dbm.ndbm.</code><code class="descname">error</code><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)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.ndbm</span></code></a>-specific errors, such as I/O errors. <a class="reference internal" href="exceptions.html#KeyError" title="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="data"> <dt id="dbm.ndbm.library"> <code class="descclassname">dbm.ndbm.</code><code class="descname">library</code><a class="headerlink" href="#dbm.ndbm.library" title="Permalink to this definition">¶</a></dt> <dd><p>Name of the <code class="docutils literal notranslate"><span class="pre">ndbm</span></code> implementation library used.</p> </dd></dl> <dl class="function"> <dt id="dbm.ndbm.open"> <code class="descclassname">dbm.ndbm.</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="#dbm.ndbm.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open a dbm database and return a <code class="docutils literal notranslate"><span class="pre">ndbm</span></code> object. The <em>filename</em> argument is the name of the database file (without the <code class="file docutils literal notranslate"><span class="pre">.dir</span></code> or <code class="file docutils literal notranslate"><span class="pre">.pag</span></code> 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 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 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">0o666</span></code> (and will be modified by the prevailing umask).</p> <p>In addition to the dictionary-like methods, <code class="docutils literal notranslate"><span class="pre">ndbm</span></code> objects provide the following method:</p> <dl class="method"> <dt id="dbm.ndbm.ndbm.close"> <code class="descclassname">ndbm.</code><code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#dbm.ndbm.ndbm.close" title="Permalink to this definition">¶</a></dt> <dd><p>Close the <code class="docutils literal notranslate"><span class="pre">ndbm</span></code> database.</p> </dd></dl> </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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.dumb</span></code></a> — Portable DBM implementation<a class="headerlink" href="#module-dbm.dumb" title="Permalink to this headline">¶</a></h2> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/dbm/dumb.py">Lib/dbm/dumb.py</a></p> <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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.dumb</span></code></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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm</span></code></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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.dumb</span></code></a> module is not written for speed and is not nearly as heavily used as the other database modules.</p> </div> <hr class="docutils" /> <p>The <a class="reference internal" href="#module-dbm.dumb" title="dbm.dumb: Portable implementation of the simple DBM interface."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.dumb</span></code></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)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code></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><code class="descclassname">dbm.dumb.</code><code class="descname">error</code><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."><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.dumb</span></code></a>-specific errors, such as I/O errors. <a class="reference internal" href="exceptions.html#KeyError" title="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="dbm.dumb.open"> <code class="descclassname">dbm.dumb.</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="#dbm.dumb.open" title="Permalink to this definition">¶</a></dt> <dd><p>Open a <code class="docutils literal notranslate"><span class="pre">dumbdbm</span></code> 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 <code class="file docutils literal notranslate"><span class="pre">.dat</span></code> and <code class="file docutils literal notranslate"><span class="pre">.dir</span></code> extensions are created.</p> <p>The optional <em>flag</em> argument supports only the semantics of <code class="docutils literal notranslate"><span class="pre">'c'</span></code> and <code class="docutils literal notranslate"><span class="pre">'n'</span></code> values. Other values will default to database being 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 <code class="docutils literal notranslate"><span class="pre">0o666</span></code> (and will be modified by the prevailing umask).</p> <div class="versionchanged"> <p><span class="versionmodified">Changed in version 3.5: </span><a class="reference internal" href="#dbm.dumb.open" title="dbm.dumb.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a> always creates a new database when the flag has the value <code class="docutils literal notranslate"><span class="pre">'n'</span></code>.</p> </div> <div class="deprecated-removed"> <p><span class="versionmodified">Deprecated since version 3.6, will be removed in version 3.8: </span>Creating database in <code class="docutils literal notranslate"><span class="pre">'r'</span></code> and <code class="docutils literal notranslate"><span class="pre">'w'</span></code> modes. Modifying database in <code class="docutils literal notranslate"><span class="pre">'r'</span></code> mode.</p> </div> <p>In addition to the methods provided by the <a class="reference internal" href="collections.abc.html#collections.abc.MutableMapping" title="collections.abc.MutableMapping"><code class="xref py py-class docutils literal notranslate"><span class="pre">collections.abc.MutableMapping</span></code></a> class, <code class="xref py py-class docutils literal notranslate"><span class="pre">dumbdbm</span></code> objects provide the following methods:</p> <dl class="method"> <dt id="dbm.dumb.dumbdbm.sync"> <code class="descclassname">dumbdbm.</code><code class="descname">sync</code><span class="sig-paren">(</span><span class="sig-paren">)</span><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 <code class="xref py py-meth docutils literal notranslate"><span class="pre">Shelve.sync()</span></code> method.</p> </dd></dl> <dl class="method"> <dt id="dbm.dumb.dumbdbm.close"> <code class="descclassname">dumbdbm.</code><code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#dbm.dumb.dumbdbm.close" title="Permalink to this definition">¶</a></dt> <dd><p>Close the <code class="docutils literal notranslate"><span class="pre">dumbdbm</span></code> database.</p> </dd></dl> </dd></dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">12.5. <code class="docutils literal notranslate"><span class="pre">dbm</span></code> — Interfaces to Unix “databases”</a><ul> <li><a class="reference internal" href="#module-dbm.gnu">12.5.1. <code class="docutils literal notranslate"><span class="pre">dbm.gnu</span></code> — GNU’s reinterpretation of dbm</a></li> <li><a class="reference internal" href="#module-dbm.ndbm">12.5.2. <code class="docutils literal notranslate"><span class="pre">dbm.ndbm</span></code> — Interface based on ndbm</a></li> <li><a class="reference internal" href="#module-dbm.dumb">12.5.3. <code class="docutils literal notranslate"><span class="pre">dbm.dumb</span></code> — Portable DBM implementation</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="marshal.html" title="previous chapter">12.4. <code class="docutils literal notranslate"><span class="pre">marshal</span></code> — Internal Python object serialization</a></p> <h4>Next topic</h4> <p class="topless"><a href="sqlite3.html" title="next chapter">12.6. <code class="docutils literal notranslate"><span class="pre">sqlite3</span></code> — DB-API 2.0 interface for SQLite databases</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.6/Doc/library/dbm.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </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="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="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">3.6.7 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" >12. 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