mirror of
https://github.com/bunny-lab-io/Borealis.git
synced 2025-11-03 19:41:57 -07:00
535 lines
40 KiB
HTML
535 lines
40 KiB
HTML
<!DOCTYPE html>
|
||
|
||
<html lang="en" data-content_root="../">
|
||
<head>
|
||
<meta charset="utf-8" />
|
||
<meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" />
|
||
<meta property="og:title" content="shelve — Python object persistence" />
|
||
<meta property="og:type" content="website" />
|
||
<meta property="og:url" content="https://docs.python.org/3/library/shelve.html" />
|
||
<meta property="og:site_name" content="Python documentation" />
|
||
<meta property="og:description" content="Source code: Lib/shelve.py A “shelf” is a persistent, dictionary-like object. The difference with “dbm” databases is that the values (not the keys!) in a shelf can be essentially arbitrary Python o..." />
|
||
<meta property="og:image" content="https://docs.python.org/3/_static/og-image.png" />
|
||
<meta property="og:image:alt" content="Python documentation" />
|
||
<meta name="description" content="Source code: Lib/shelve.py A “shelf” is a persistent, dictionary-like object. The difference with “dbm” databases is that the values (not the keys!) in a shelf can be essentially arbitrary Python o..." />
|
||
<meta property="og:image:width" content="200">
|
||
<meta property="og:image:height" content="200">
|
||
<meta name="theme-color" content="#3776ab">
|
||
|
||
<title>shelve — Python object persistence — Python 3.13.3 documentation</title><meta name="viewport" content="width=device-width, initial-scale=1.0">
|
||
|
||
<link rel="stylesheet" type="text/css" href="../_static/pygments.css?v=b86133f3" />
|
||
<link rel="stylesheet" type="text/css" href="../_static/pydoctheme.css?v=23252803" />
|
||
<link id="pygments_dark_css" media="(prefers-color-scheme: dark)" rel="stylesheet" type="text/css" href="../_static/pygments_dark.css?v=5349f25f" />
|
||
|
||
<script src="../_static/documentation_options.js?v=5d57ca2d"></script>
|
||
<script src="../_static/doctools.js?v=9bcbadda"></script>
|
||
<script src="../_static/sphinx_highlight.js?v=dc90522c"></script>
|
||
|
||
<script src="../_static/sidebar.js"></script>
|
||
|
||
<link rel="search" type="application/opensearchdescription+xml"
|
||
title="Search within Python 3.13.3 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="marshal — Internal Python object serialization" href="marshal.html" />
|
||
<link rel="prev" title="copyreg — Register pickle support functions" href="copyreg.html" />
|
||
|
||
<link rel="canonical" href="https://docs.python.org/3/library/shelve.html">
|
||
|
||
|
||
|
||
|
||
|
||
<style>
|
||
@media only screen {
|
||
table.full-width-table {
|
||
width: 100%;
|
||
}
|
||
}
|
||
</style>
|
||
<link rel="stylesheet" href="../_static/pydoctheme_dark.css" media="(prefers-color-scheme: dark)" id="pydoctheme_dark_css">
|
||
<link rel="shortcut icon" type="image/png" href="../_static/py.svg" />
|
||
<script type="text/javascript" src="../_static/copybutton.js"></script>
|
||
<script type="text/javascript" src="../_static/menu.js"></script>
|
||
<script type="text/javascript" src="../_static/search-focus.js"></script>
|
||
<script type="text/javascript" src="../_static/themetoggle.js"></script>
|
||
<script type="text/javascript" src="../_static/rtd_switcher.js"></script>
|
||
<meta name="readthedocs-addons-api-version" content="1">
|
||
|
||
</head>
|
||
<body>
|
||
<div class="mobile-nav">
|
||
<input type="checkbox" id="menuToggler" class="toggler__input" aria-controls="navigation"
|
||
aria-pressed="false" aria-expanded="false" role="button" aria-label="Menu" />
|
||
<nav class="nav-content" role="navigation">
|
||
<label for="menuToggler" class="toggler__label">
|
||
<span></span>
|
||
</label>
|
||
<span class="nav-items-wrapper">
|
||
<a href="https://www.python.org/" class="nav-logo">
|
||
<img src="../_static/py.svg" alt="Python logo"/>
|
||
</a>
|
||
<span class="version_switcher_placeholder"></span>
|
||
<form role="search" class="search" action="../search.html" method="get">
|
||
<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" class="search-icon">
|
||
<path fill-rule="nonzero" fill="currentColor" d="M15.5 14h-.79l-.28-.27a6.5 6.5 0 001.48-5.34c-.47-2.78-2.79-5-5.59-5.34a6.505 6.505 0 00-7.27 7.27c.34 2.8 2.56 5.12 5.34 5.59a6.5 6.5 0 005.34-1.48l.27.28v.79l4.25 4.25c.41.41 1.08.41 1.49 0 .41-.41.41-1.08 0-1.49L15.5 14zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"></path>
|
||
</svg>
|
||
<input placeholder="Quick search" aria-label="Quick search" type="search" name="q" />
|
||
<input type="submit" value="Go"/>
|
||
</form>
|
||
</span>
|
||
</nav>
|
||
<div class="menu-wrapper">
|
||
<nav class="menu" role="navigation" aria-label="main navigation">
|
||
<div class="language_switcher_placeholder"></div>
|
||
|
||
<label class="theme-selector-label">
|
||
Theme
|
||
<select class="theme-selector" oninput="activateTheme(this.value)">
|
||
<option value="auto" selected>Auto</option>
|
||
<option value="light">Light</option>
|
||
<option value="dark">Dark</option>
|
||
</select>
|
||
</label>
|
||
<div>
|
||
<h3><a href="../contents.html">Table of Contents</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code> — Python object persistence</a><ul>
|
||
<li><a class="reference internal" href="#restrictions">Restrictions</a></li>
|
||
<li><a class="reference internal" href="#example">Example</a></li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
|
||
</div>
|
||
<div>
|
||
<h4>Previous topic</h4>
|
||
<p class="topless"><a href="copyreg.html"
|
||
title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">copyreg</span></code> — Register <code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code> support functions</a></p>
|
||
</div>
|
||
<div>
|
||
<h4>Next topic</h4>
|
||
<p class="topless"><a href="marshal.html"
|
||
title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">marshal</span></code> — Internal Python object serialization</a></p>
|
||
</div>
|
||
<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/main/Doc/library/shelve.rst"
|
||
rel="nofollow">Show Source
|
||
</a>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</nav>
|
||
</div>
|
||
</div>
|
||
|
||
|
||
<div class="related" role="navigation" aria-label="Related">
|
||
<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="marshal.html" title="marshal — Internal Python object serialization"
|
||
accesskey="N">next</a> |</li>
|
||
<li class="right" >
|
||
<a href="copyreg.html" title="copyreg — Register pickle support functions"
|
||
accesskey="P">previous</a> |</li>
|
||
|
||
<li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li>
|
||
<li><a href="https://www.python.org/">Python</a> »</li>
|
||
<li class="switchers">
|
||
<div class="language_switcher_placeholder"></div>
|
||
<div class="version_switcher_placeholder"></div>
|
||
</li>
|
||
<li>
|
||
|
||
</li>
|
||
<li id="cpython-language-and-version">
|
||
<a href="../index.html">3.13.3 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">Data Persistence</a> »</li>
|
||
<li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code> — Python object persistence</a></li>
|
||
<li class="right">
|
||
|
||
|
||
<div class="inline-search" role="search">
|
||
<form class="inline-search" action="../search.html" method="get">
|
||
<input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" />
|
||
<input type="submit" value="Go" />
|
||
</form>
|
||
</div>
|
||
|
|
||
</li>
|
||
<li class="right">
|
||
<label class="theme-selector-label">
|
||
Theme
|
||
<select class="theme-selector" oninput="activateTheme(this.value)">
|
||
<option value="auto" selected>Auto</option>
|
||
<option value="light">Light</option>
|
||
<option value="dark">Dark</option>
|
||
</select>
|
||
</label> |</li>
|
||
|
||
</ul>
|
||
</div>
|
||
|
||
<div class="document">
|
||
<div class="documentwrapper">
|
||
<div class="bodywrapper">
|
||
<div class="body" role="main">
|
||
|
||
<section id="module-shelve">
|
||
<span id="shelve-python-object-persistence"></span><h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code> — Python object persistence<a class="headerlink" href="#module-shelve" title="Link to this heading">¶</a></h1>
|
||
<p><strong>Source code:</strong> <a class="extlink-source reference external" href="https://github.com/python/cpython/tree/3.13/Lib/shelve.py">Lib/shelve.py</a></p>
|
||
<hr class="docutils" id="index-0" />
|
||
<p>A “shelf” is a persistent, dictionary-like object. The difference with “dbm”
|
||
databases is that the values (not the keys!) in a shelf can be essentially
|
||
arbitrary Python objects — anything that the <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> module can handle.
|
||
This includes most class instances, recursive data types, and objects containing
|
||
lots of shared sub-objects. The keys are ordinary strings.</p>
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="shelve.open">
|
||
<span class="sig-prename descclassname"><span class="pre">shelve.</span></span><span class="sig-name descname"><span class="pre">open</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">filename</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">flag</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'c'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">protocol</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">writeback</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#shelve.open" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Open a persistent dictionary. The filename specified is the base filename for
|
||
the underlying database. As a side-effect, an extension may be added to the
|
||
filename and more than one file may be created. By default, the underlying
|
||
database file is opened for reading and writing. The optional <em>flag</em> parameter
|
||
has the same interpretation as the <em>flag</em> parameter of <a class="reference internal" href="dbm.html#dbm.open" title="dbm.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">dbm.open()</span></code></a>.</p>
|
||
<p>By default, pickles created with <a class="reference internal" href="pickle.html#pickle.DEFAULT_PROTOCOL" title="pickle.DEFAULT_PROTOCOL"><code class="xref py py-const docutils literal notranslate"><span class="pre">pickle.DEFAULT_PROTOCOL</span></code></a> are used
|
||
to serialize values. The version of the pickle protocol can be specified
|
||
with the <em>protocol</em> parameter.</p>
|
||
<p>Because of Python semantics, a shelf cannot know when a mutable
|
||
persistent-dictionary entry is modified. By default modified objects are
|
||
written <em>only</em> when assigned to the shelf (see <a class="reference internal" href="#shelve-example"><span class="std std-ref">Example</span></a>). If the
|
||
optional <em>writeback</em> parameter is set to <code class="docutils literal notranslate"><span class="pre">True</span></code>, all entries accessed are also
|
||
cached in memory, and written back on <a class="reference internal" href="#shelve.Shelf.sync" title="shelve.Shelf.sync"><code class="xref py py-meth docutils literal notranslate"><span class="pre">sync()</span></code></a> and
|
||
<a class="reference internal" href="#shelve.Shelf.close" title="shelve.Shelf.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a>; this can make it handier to mutate mutable entries in
|
||
the persistent dictionary, but, if many entries are accessed, it can consume
|
||
vast amounts of memory for the cache, and it can make the close operation
|
||
very slow since all accessed entries are written back (there is no way to
|
||
determine which accessed entries are mutable, nor which ones were actually
|
||
mutated).</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.10: </span><a class="reference internal" href="pickle.html#pickle.DEFAULT_PROTOCOL" title="pickle.DEFAULT_PROTOCOL"><code class="xref py py-const docutils literal notranslate"><span class="pre">pickle.DEFAULT_PROTOCOL</span></code></a> is now used as the default pickle
|
||
protocol.</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.11: </span>Accepts <a class="reference internal" href="../glossary.html#term-path-like-object"><span class="xref std std-term">path-like object</span></a> for filename.</p>
|
||
</div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">Note</p>
|
||
<p>Do not rely on the shelf being closed automatically; always call
|
||
<a class="reference internal" href="#shelve.Shelf.close" title="shelve.Shelf.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a> explicitly when you don’t need it any more, or
|
||
use <a class="reference internal" href="#shelve.open" title="shelve.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">shelve.open()</span></code></a> as a context manager:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">with</span> <span class="n">shelve</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="s1">'spam'</span><span class="p">)</span> <span class="k">as</span> <span class="n">db</span><span class="p">:</span>
|
||
<span class="n">db</span><span class="p">[</span><span class="s1">'eggs'</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'eggs'</span>
|
||
</pre></div>
|
||
</div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<div class="admonition warning" id="shelve-security">
|
||
<p class="admonition-title">Warning</p>
|
||
<p>Because the <a class="reference internal" href="#module-shelve" title="shelve: Python object persistence."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code></a> module is backed by <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a>, it is insecure
|
||
to load a shelf from an untrusted source. Like with pickle, loading a shelf
|
||
can execute arbitrary code.</p>
|
||
</div>
|
||
<p>Shelf objects support most of methods and operations supported by dictionaries
|
||
(except copying, constructors and operators <code class="docutils literal notranslate"><span class="pre">|</span></code> and <code class="docutils literal notranslate"><span class="pre">|=</span></code>). This eases the
|
||
transition from dictionary based scripts to those requiring persistent storage.</p>
|
||
<p>Two additional methods are supported:</p>
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="shelve.Shelf.sync">
|
||
<span class="sig-prename descclassname"><span class="pre">Shelf.</span></span><span class="sig-name descname"><span class="pre">sync</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#shelve.Shelf.sync" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Write back all entries in the cache if the shelf was opened with <em>writeback</em>
|
||
set to <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate"><span class="pre">True</span></code></a>. Also empty the cache and synchronize the persistent
|
||
dictionary on disk, if feasible. This is called automatically when the shelf
|
||
is closed with <a class="reference internal" href="#shelve.Shelf.close" title="shelve.Shelf.close"><code class="xref py py-meth docutils literal notranslate"><span class="pre">close()</span></code></a>.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py method">
|
||
<dt class="sig sig-object py" id="shelve.Shelf.close">
|
||
<span class="sig-prename descclassname"><span class="pre">Shelf.</span></span><span class="sig-name descname"><span class="pre">close</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#shelve.Shelf.close" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Synchronize and close the persistent <em>dict</em> object. Operations on a closed
|
||
shelf will fail with a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>.</p>
|
||
</dd></dl>
|
||
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<p><a class="reference external" href="https://code.activestate.com/recipes/576642-persistent-dict-with-multiple-standard-file-format/">Persistent dictionary recipe</a>
|
||
with widely supported storage formats and having the speed of native
|
||
dictionaries.</p>
|
||
</div>
|
||
<section id="restrictions">
|
||
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Link to this heading">¶</a></h2>
|
||
<ul class="simple" id="index-1">
|
||
<li><p>The choice of which database package will be used (such as <a class="reference internal" href="dbm.html#module-dbm.ndbm" title="dbm.ndbm: The New Database Manager (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.ndbm</span></code></a> or
|
||
<a class="reference internal" href="dbm.html#module-dbm.gnu" title="dbm.gnu: GNU database manager (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.gnu</span></code></a>) depends on which interface is available. Therefore it is not
|
||
safe to open the database directly using <a class="reference internal" href="dbm.html#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>. The database is also
|
||
(unfortunately) subject to the limitations of <a class="reference internal" href="dbm.html#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>, if it is used —
|
||
this means that (the pickled representation of) the objects stored in the
|
||
database should be fairly small, and in rare cases key collisions may cause
|
||
the database to refuse updates.</p></li>
|
||
<li><p>The <a class="reference internal" href="#module-shelve" title="shelve: Python object persistence."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code></a> module does not support <em>concurrent</em> read/write access to
|
||
shelved objects. (Multiple simultaneous read accesses are safe.) When a
|
||
program has a shelf open for writing, no other program should have it open for
|
||
reading or writing. Unix file locking can be used to solve this, but this
|
||
differs across Unix versions and requires knowledge about the database
|
||
implementation used.</p></li>
|
||
<li><p>On macOS <a class="reference internal" href="dbm.html#module-dbm.ndbm" title="dbm.ndbm: The New Database Manager (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">dbm.ndbm</span></code></a> can silently corrupt the database file on updates,
|
||
which can cause hard crashes when trying to read from the database.</p></li>
|
||
</ul>
|
||
<dl class="py class">
|
||
<dt class="sig sig-object py" id="shelve.Shelf">
|
||
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">shelve.</span></span><span class="sig-name descname"><span class="pre">Shelf</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dict</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">protocol</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">writeback</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">keyencoding</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'utf-8'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#shelve.Shelf" title="Link to this definition">¶</a></dt>
|
||
<dd><p>A subclass of <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> which stores pickled
|
||
values in the <em>dict</em> object.</p>
|
||
<p>By default, pickles created with <a class="reference internal" href="pickle.html#pickle.DEFAULT_PROTOCOL" title="pickle.DEFAULT_PROTOCOL"><code class="xref py py-const docutils literal notranslate"><span class="pre">pickle.DEFAULT_PROTOCOL</span></code></a> are used
|
||
to serialize values. The version of the pickle protocol can be specified
|
||
with the <em>protocol</em> parameter. See the <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a> documentation for a
|
||
discussion of the pickle protocols.</p>
|
||
<p>If the <em>writeback</em> parameter is <code class="docutils literal notranslate"><span class="pre">True</span></code>, the object will hold a cache of all
|
||
entries accessed and write them back to the <em>dict</em> at sync and close times.
|
||
This allows natural operations on mutable entries, but can consume much more
|
||
memory and make sync and close take a long time.</p>
|
||
<p>The <em>keyencoding</em> parameter is the encoding used to encode keys before they
|
||
are used with the underlying dict.</p>
|
||
<p>A <a class="reference internal" href="#shelve.Shelf" title="shelve.Shelf"><code class="xref py py-class docutils literal notranslate"><span class="pre">Shelf</span></code></a> object can also be used as a context manager, in which
|
||
case it will be automatically closed when the <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> block ends.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.2: </span>Added the <em>keyencoding</em> parameter; previously, keys were always encoded in
|
||
UTF-8.</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.4: </span>Added context manager support.</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.10: </span><a class="reference internal" href="pickle.html#pickle.DEFAULT_PROTOCOL" title="pickle.DEFAULT_PROTOCOL"><code class="xref py py-const docutils literal notranslate"><span class="pre">pickle.DEFAULT_PROTOCOL</span></code></a> is now used as the default pickle
|
||
protocol.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py class">
|
||
<dt class="sig sig-object py" id="shelve.BsdDbShelf">
|
||
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">shelve.</span></span><span class="sig-name descname"><span class="pre">BsdDbShelf</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">dict</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">protocol</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">writeback</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">keyencoding</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'utf-8'</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#shelve.BsdDbShelf" title="Link to this definition">¶</a></dt>
|
||
<dd><p>A subclass of <a class="reference internal" href="#shelve.Shelf" title="shelve.Shelf"><code class="xref py py-class docutils literal notranslate"><span class="pre">Shelf</span></code></a> which exposes <code class="xref py py-meth docutils literal notranslate"><span class="pre">first()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">next()</span></code>,
|
||
<code class="xref py py-meth docutils literal notranslate"><span class="pre">previous()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">last()</span></code> and <code class="xref py py-meth docutils literal notranslate"><span class="pre">set_location()</span></code> methods.
|
||
These are available
|
||
in the third-party <code class="xref py py-mod docutils literal notranslate"><span class="pre">bsddb</span></code> module from <a class="reference external" href="https://www.jcea.es/programacion/pybsddb.htm">pybsddb</a> but not in other database
|
||
modules. The <em>dict</em> object passed to the constructor must support those
|
||
methods. This is generally accomplished by calling one of
|
||
<code class="xref py py-func docutils literal notranslate"><span class="pre">bsddb.hashopen()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">bsddb.btopen()</span></code> or <code class="xref py py-func docutils literal notranslate"><span class="pre">bsddb.rnopen()</span></code>. The
|
||
optional <em>protocol</em>, <em>writeback</em>, and <em>keyencoding</em> parameters have the same
|
||
interpretation as for the <a class="reference internal" href="#shelve.Shelf" title="shelve.Shelf"><code class="xref py py-class docutils literal notranslate"><span class="pre">Shelf</span></code></a> class.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py class">
|
||
<dt class="sig sig-object py" id="shelve.DbfilenameShelf">
|
||
<em class="property"><span class="k"><span class="pre">class</span></span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">shelve.</span></span><span class="sig-name descname"><span class="pre">DbfilenameShelf</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">filename</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">flag</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'c'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">protocol</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">writeback</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#shelve.DbfilenameShelf" title="Link to this definition">¶</a></dt>
|
||
<dd><p>A subclass of <a class="reference internal" href="#shelve.Shelf" title="shelve.Shelf"><code class="xref py py-class docutils literal notranslate"><span class="pre">Shelf</span></code></a> which accepts a <em>filename</em> instead of a dict-like
|
||
object. The underlying file will be opened using <a class="reference internal" href="dbm.html#dbm.open" title="dbm.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">dbm.open()</span></code></a>. By
|
||
default, the file will be created and opened for both read and write. The
|
||
optional <em>flag</em> parameter has the same interpretation as for the <a class="reference internal" href="#shelve.open" title="shelve.open"><code class="xref py py-func docutils literal notranslate"><span class="pre">open()</span></code></a>
|
||
function. The optional <em>protocol</em> and <em>writeback</em> parameters have the same
|
||
interpretation as for the <a class="reference internal" href="#shelve.Shelf" title="shelve.Shelf"><code class="xref py py-class docutils literal notranslate"><span class="pre">Shelf</span></code></a> class.</p>
|
||
</dd></dl>
|
||
|
||
</section>
|
||
<section id="example">
|
||
<span id="shelve-example"></span><h2>Example<a class="headerlink" href="#example" title="Link to this heading">¶</a></h2>
|
||
<p>To summarize the interface (<code class="docutils literal notranslate"><span class="pre">key</span></code> is a string, <code class="docutils literal notranslate"><span class="pre">data</span></code> is an arbitrary
|
||
object):</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </span><span class="nn">shelve</span>
|
||
|
||
<span class="n">d</span> <span class="o">=</span> <span class="n">shelve</span><span class="o">.</span><span class="n">open</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span> <span class="c1"># open -- file may get suffix added by low-level</span>
|
||
<span class="c1"># library</span>
|
||
|
||
<span class="n">d</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="o">=</span> <span class="n">data</span> <span class="c1"># store data at key (overwrites old data if</span>
|
||
<span class="c1"># using an existing key)</span>
|
||
<span class="n">data</span> <span class="o">=</span> <span class="n">d</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="c1"># retrieve a COPY of data at key (raise KeyError</span>
|
||
<span class="c1"># if no such key)</span>
|
||
<span class="k">del</span> <span class="n">d</span><span class="p">[</span><span class="n">key</span><span class="p">]</span> <span class="c1"># delete data stored at key (raises KeyError</span>
|
||
<span class="c1"># if no such key)</span>
|
||
|
||
<span class="n">flag</span> <span class="o">=</span> <span class="n">key</span> <span class="ow">in</span> <span class="n">d</span> <span class="c1"># true if the key exists</span>
|
||
<span class="n">klist</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">d</span><span class="o">.</span><span class="n">keys</span><span class="p">())</span> <span class="c1"># a list of all existing keys (slow!)</span>
|
||
|
||
<span class="c1"># as d was opened WITHOUT writeback=True, beware:</span>
|
||
<span class="n">d</span><span class="p">[</span><span class="s1">'xx'</span><span class="p">]</span> <span class="o">=</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">]</span> <span class="c1"># this works as expected, but...</span>
|
||
<span class="n">d</span><span class="p">[</span><span class="s1">'xx'</span><span class="p">]</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span> <span class="c1"># *this doesn't!* -- d['xx'] is STILL [0, 1, 2]!</span>
|
||
|
||
<span class="c1"># having opened d without writeback=True, you need to code carefully:</span>
|
||
<span class="n">temp</span> <span class="o">=</span> <span class="n">d</span><span class="p">[</span><span class="s1">'xx'</span><span class="p">]</span> <span class="c1"># extracts the copy</span>
|
||
<span class="n">temp</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span> <span class="c1"># mutates the copy</span>
|
||
<span class="n">d</span><span class="p">[</span><span class="s1">'xx'</span><span class="p">]</span> <span class="o">=</span> <span class="n">temp</span> <span class="c1"># stores the copy right back, to persist it</span>
|
||
|
||
<span class="c1"># or, d=shelve.open(filename,writeback=True) would let you just code</span>
|
||
<span class="c1"># d['xx'].append(5) and have it work as expected, BUT it would also</span>
|
||
<span class="c1"># consume more memory and make the d.close() operation slower.</span>
|
||
|
||
<span class="n">d</span><span class="o">.</span><span class="n">close</span><span class="p">()</span> <span class="c1"># close it</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt>Module <a class="reference internal" href="dbm.html#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></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="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code></a></dt><dd><p>Object serialization used by <a class="reference internal" href="#module-shelve" title="shelve: Python object persistence."><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code></a>.</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</section>
|
||
</section>
|
||
|
||
|
||
<div class="clearer"></div>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="sphinxsidebar" role="navigation" aria-label="Main">
|
||
<div class="sphinxsidebarwrapper">
|
||
<div>
|
||
<h3><a href="../contents.html">Table of Contents</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code> — Python object persistence</a><ul>
|
||
<li><a class="reference internal" href="#restrictions">Restrictions</a></li>
|
||
<li><a class="reference internal" href="#example">Example</a></li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
|
||
</div>
|
||
<div>
|
||
<h4>Previous topic</h4>
|
||
<p class="topless"><a href="copyreg.html"
|
||
title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">copyreg</span></code> — Register <code class="xref py py-mod docutils literal notranslate"><span class="pre">pickle</span></code> support functions</a></p>
|
||
</div>
|
||
<div>
|
||
<h4>Next topic</h4>
|
||
<p class="topless"><a href="marshal.html"
|
||
title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">marshal</span></code> — Internal Python object serialization</a></p>
|
||
</div>
|
||
<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/main/Doc/library/shelve.rst"
|
||
rel="nofollow">Show Source
|
||
</a>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
<div id="sidebarbutton" title="Collapse sidebar">
|
||
<span>«</span>
|
||
</div>
|
||
|
||
</div>
|
||
<div class="clearer"></div>
|
||
</div>
|
||
<div class="related" role="navigation" aria-label="Related">
|
||
<h3>Navigation</h3>
|
||
<ul>
|
||
<li class="right" style="margin-right: 10px">
|
||
<a href="../genindex.html" title="General Index"
|
||
>index</a></li>
|
||
<li class="right" >
|
||
<a href="../py-modindex.html" title="Python Module Index"
|
||
>modules</a> |</li>
|
||
<li class="right" >
|
||
<a href="marshal.html" title="marshal — Internal Python object serialization"
|
||
>next</a> |</li>
|
||
<li class="right" >
|
||
<a href="copyreg.html" title="copyreg — Register pickle support functions"
|
||
>previous</a> |</li>
|
||
|
||
<li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li>
|
||
<li><a href="https://www.python.org/">Python</a> »</li>
|
||
<li class="switchers">
|
||
<div class="language_switcher_placeholder"></div>
|
||
<div class="version_switcher_placeholder"></div>
|
||
</li>
|
||
<li>
|
||
|
||
</li>
|
||
<li id="cpython-language-and-version">
|
||
<a href="../index.html">3.13.3 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" >Data Persistence</a> »</li>
|
||
<li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate"><span class="pre">shelve</span></code> — Python object persistence</a></li>
|
||
<li class="right">
|
||
|
||
|
||
<div class="inline-search" role="search">
|
||
<form class="inline-search" action="../search.html" method="get">
|
||
<input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" />
|
||
<input type="submit" value="Go" />
|
||
</form>
|
||
</div>
|
||
|
|
||
</li>
|
||
<li class="right">
|
||
<label class="theme-selector-label">
|
||
Theme
|
||
<select class="theme-selector" oninput="activateTheme(this.value)">
|
||
<option value="auto" selected>Auto</option>
|
||
<option value="light">Light</option>
|
||
<option value="dark">Dark</option>
|
||
</select>
|
||
</label> |</li>
|
||
|
||
</ul>
|
||
</div>
|
||
<div class="footer">
|
||
©
|
||
<a href="../copyright.html">
|
||
|
||
Copyright
|
||
|
||
</a>
|
||
2001-2025, Python Software Foundation.
|
||
<br />
|
||
This page is licensed under the Python Software Foundation License Version 2.
|
||
<br />
|
||
Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License.
|
||
<br />
|
||
|
||
See <a href="/license.html">History and License</a> for more information.<br />
|
||
|
||
|
||
<br />
|
||
|
||
The Python Software Foundation is a non-profit corporation.
|
||
<a href="https://www.python.org/psf/donations/">Please donate.</a>
|
||
<br />
|
||
<br />
|
||
Last updated on Apr 08, 2025 (14:33 UTC).
|
||
|
||
<a href="/bugs.html">Found a bug</a>?
|
||
|
||
<br />
|
||
|
||
Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 8.2.3.
|
||
</div>
|
||
|
||
</body>
|
||
</html> |