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<div class="section" id="module-dbm">
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<span id="dbm-interfaces-to-unix-databases"></span><h1><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>
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<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/dbm/__init__.py">Lib/dbm/__init__.py</a></p>
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<hr class="docutils" />
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<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 —
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<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
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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
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is a <a class="reference external" href="https://www.jcea.es/programacion/pybsddb.htm">third party interface</a> to
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the Oracle Berkeley DB.</p>
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<dl class="exception">
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<dt id="dbm.error">
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<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>
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<dd><p>A tuple containing the exceptions that can be raised by each of the supported
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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
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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>
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</dd></dl>
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<dl class="function">
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<dt id="dbm.whichdb">
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<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>
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<dd><p>This function attempts to guess which of the several simple database modules
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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
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be used to open a given file.</p>
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<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
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because it’s unreadable or doesn’t exist; the empty string (<code class="docutils literal notranslate"><span class="pre">''</span></code>) if the
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file’s format can’t be guessed; or a string containing the required module
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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>
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</dd></dl>
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<dl class="function">
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<dt id="dbm.open">
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<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>
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<dd><p>Open the database file <em>file</em> and return a corresponding object.</p>
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<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
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determine its type and the appropriate module is used; if it does not exist,
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the first module listed above that can be imported is used.</p>
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<p>The optional <em>flag</em> argument can be:</p>
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<table class="docutils align-center">
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<colgroup>
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<col style="width: 17%" />
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<col style="width: 83%" />
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</colgroup>
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<thead>
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<tr class="row-odd"><th class="head"><p>Value</p></th>
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<th class="head"><p>Meaning</p></th>
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</tr>
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</thead>
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<tbody>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'r'</span></code></p></td>
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<td><p>Open existing database for reading only
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(default)</p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'w'</span></code></p></td>
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<td><p>Open existing database for reading and
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writing</p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'c'</span></code></p></td>
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<td><p>Open database for reading and writing,
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creating it if it doesn’t exist</p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'n'</span></code></p></td>
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<td><p>Always create a new, empty database, open
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for reading and writing</p></td>
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</tr>
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</tbody>
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</table>
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<p>The optional <em>mode</em> argument is the Unix mode of the file, used only when the
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database has to be created. It defaults to octal <code class="docutils literal notranslate"><span class="pre">0o666</span></code> (and will be
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modified by the prevailing umask).</p>
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</dd></dl>
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<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
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dictionaries; keys and their corresponding values can be stored, retrieved, and
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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
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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>
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<div class="versionchanged">
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<p><span class="versionmodified changed">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>
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</div>
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<p>Key and values are always stored as bytes. This means that when
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strings are used they are implicitly converted to the default encoding before
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being stored.</p>
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<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
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will automatically close them when done.</p>
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<div class="versionchanged">
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<p><span class="versionmodified changed">Changed in version 3.4: </span>Added native support for the context management protocol to the objects
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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>
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</div>
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<p>The following example records some hostnames and a corresponding title, and
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then prints out the contents of the database:</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">dbm</span>
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<span class="c1"># Open database, creating it if necessary.</span>
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<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>
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<span class="c1"># Record some values</span>
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<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>
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<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>
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<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>
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<span class="c1"># Note that the keys are considered bytes now.</span>
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<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>
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<span class="c1"># Notice how the value is now in bytes.</span>
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<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>
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<span class="c1"># Often-used methods of the dict interface work too.</span>
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<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>
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<span class="c1"># Storing a non-string key or value will raise an exception (most</span>
|
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|
<span class="c1"># likely a TypeError).</span>
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<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>
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<span class="c1"># db is automatically closed when leaving the with statement.</span>
|
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</pre></div>
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</div>
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<div class="admonition seealso">
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<p class="admonition-title">See also</p>
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<dl class="simple">
|
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|
<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><p>Persistence module which stores non-string data.</p>
|
|
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</dd>
|
|
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</dl>
|
|
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</div>
|
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<p>The individual submodules are described in the following sections.</p>
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<div class="section" id="module-dbm.gnu">
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|
|
<span id="dbm-gnu-gnu-s-reinterpretation-of-dbm"></span><h2><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>
|
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|
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/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
|
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|
<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>
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<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.
|
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|
<code class="docutils literal notranslate"><span class="pre">dbm.gnu.gdbm</span></code> objects behave like mappings (dictionaries), except that keys and
|
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|
values are always converted to bytes before storing. Printing a <code class="docutils literal notranslate"><span class="pre">gdbm</span></code>
|
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|
object doesn’t print the
|
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|
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
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supported.</p>
|
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<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>
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<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
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raised for general mapping errors like specifying an incorrect key.</p>
|
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</dd></dl>
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<dl class="function">
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<dt id="dbm.gnu.open">
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<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>
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<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>
|
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argument is the name of the database file.</p>
|
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<p>The optional <em>flag</em> argument can be:</p>
|
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<table class="docutils align-center">
|
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<colgroup>
|
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|
<col style="width: 17%" />
|
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|
<col style="width: 83%" />
|
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|
</colgroup>
|
|
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<thead>
|
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<tr class="row-odd"><th class="head"><p>Value</p></th>
|
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<th class="head"><p>Meaning</p></th>
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</tr>
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</thead>
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<tbody>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'r'</span></code></p></td>
|
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<td><p>Open existing database for reading only
|
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(default)</p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'w'</span></code></p></td>
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<td><p>Open existing database for reading and
|
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writing</p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'c'</span></code></p></td>
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<td><p>Open database for reading and writing,
|
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creating it if it doesn’t exist</p></td>
|
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'n'</span></code></p></td>
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<td><p>Always create a new, empty database, open
|
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|
for reading and writing</p></td>
|
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|
</tr>
|
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|
</tbody>
|
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</table>
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<p>The following additional characters may be appended to the flag to control
|
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how the database is opened:</p>
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<table class="docutils align-center">
|
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|
<colgroup>
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|
<col style="width: 17%" />
|
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<col style="width: 83%" />
|
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|
</colgroup>
|
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|
<thead>
|
|
|
<tr class="row-odd"><th class="head"><p>Value</p></th>
|
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|
<th class="head"><p>Meaning</p></th>
|
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</tr>
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</thead>
|
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<tbody>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'f'</span></code></p></td>
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<td><p>Open the database in fast mode. Writes
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to the database will not be synchronized.</p></td>
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</tr>
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<tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">'s'</span></code></p></td>
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<td><p>Synchronized mode. This will cause changes
|
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to the database to be immediately written
|
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|
to the file.</p></td>
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</tr>
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<tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">'u'</span></code></p></td>
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<td><p>Do not lock database.</p></td>
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</tr>
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</tbody>
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</table>
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<p>Not all flags are valid for all versions of <code class="docutils literal notranslate"><span class="pre">gdbm</span></code>. The module constant
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<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
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<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>
|
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<p>The optional <em>mode</em> argument is the Unix mode of the file, used only when the
|
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|
database has to be created. It defaults to octal <code class="docutils literal notranslate"><span class="pre">0o666</span></code>.</p>
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<p>In addition to the dictionary-like methods, <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> objects have the
|
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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>
|
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<dd><p>It’s possible to loop over every key in the database using this method and the
|
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<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
|
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hash values, and won’t be sorted by the key values. This method returns
|
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the starting key.</p>
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</dd></dl>
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<dl class="method">
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|
<dt id="dbm.gnu.gdbm.nextkey">
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|
<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>
|
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<dd><p>Returns the key that follows <em>key</em> in the traversal. The following code prints
|
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|
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>
|
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|
<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>
|
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|
</pre></div>
|
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|
</div>
|
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|
</dd></dl>
|
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|
<dl class="method">
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|
|
<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>
|
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|
objects will not shorten the length of a database file except by using this
|
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|
reorganization; otherwise, deleted file space will be kept and reused as new
|
|
|
(key, value) pairs are added.</p>
|
|
|
</dd></dl>
|
|
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|
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|
<dl class="method">
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|
|
<dt id="dbm.gnu.gdbm.sync">
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|
|
<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>
|
|
|
|
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|
</dd></dl>
|
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|
|
|
|
</div>
|
|
|
<div class="section" id="module-dbm.ndbm">
|
|
|
<span id="dbm-ndbm-interface-based-on-ndbm"></span><h2><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/3.7/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 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 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><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/3.7/Lib/dbm/dumb.py">Lib/dbm/dumb.py</a></p>
|
|
|
<div class="admonition note" id="index-0">
|
|
|
<p class="admonition-title">Note</p>
|
|
|
<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 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="admonition warning">
|
|
|
<p class="admonition-title">Warning</p>
|
|
|
<p>It is possible to crash the Python interpreter when loading a database
|
|
|
with a sufficiently large/complex entry due to stack depth limitations in
|
|
|
Python’s AST compiler.</p>
|
|
|
</div>
|
|
|
<div class="versionchanged">
|
|
|
<p><span class="versionmodified changed">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
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<code class="docutils literal notranslate"><span class="pre">'n'</span></code>.</p>
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</div>
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<div class="deprecated">
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<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
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<code class="docutils literal notranslate"><span class="pre">'r'</span></code> mode.</p>
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</div>
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<p>In addition to the methods provided by the
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<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
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provide the following methods:</p>
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<dl class="method">
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<dt id="dbm.dumb.dumbdbm.sync">
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<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>
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<dd><p>Synchronize the on-disk directory and data files. This method is called
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by the <code class="xref py py-meth docutils literal notranslate"><span class="pre">Shelve.sync()</span></code> method.</p>
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</dd></dl>
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<dl class="method">
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<dt id="dbm.dumb.dumbdbm.close">
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<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>
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<dd><p>Close the <code class="docutils literal notranslate"><span class="pre">dumbdbm</span></code> database.</p>
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</dd></dl>
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</dd></dl>
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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm</span></code> — Interfaces to Unix “databases”</a><ul>
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<li><a class="reference internal" href="#module-dbm.gnu"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code> — GNU’s reinterpretation of dbm</a></li>
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<li><a class="reference internal" href="#module-dbm.ndbm"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.ndbm</span></code> — Interface based on ndbm</a></li>
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<li><a class="reference internal" href="#module-dbm.dumb"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.dumb</span></code> — Portable DBM implementation</a></li>
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