302 lines
17 KiB
HTML
302 lines
17 KiB
HTML
|
||
<!DOCTYPE html>
|
||
|
||
<html xmlns="http://www.w3.org/1999/xhtml" lang="zh_CN">
|
||
<head>
|
||
<meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" />
|
||
|
||
<title>copy --- 浅层 (shallow) 和深层 (deep) 复制操作 — Python 3.8.20 文档</title><meta name="viewport" content="width=device-width, initial-scale=1.0">
|
||
|
||
<link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" />
|
||
<link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
|
||
|
||
<script id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script>
|
||
<script src="../_static/jquery.js"></script>
|
||
<script src="../_static/underscore.js"></script>
|
||
<script src="../_static/doctools.js"></script>
|
||
<script src="../_static/language_data.js"></script>
|
||
<script src="../_static/translations.js"></script>
|
||
|
||
<script src="../_static/sidebar.js"></script>
|
||
|
||
<link rel="search" type="application/opensearchdescription+xml"
|
||
title="在 Python 3.8.20 文档 中搜索"
|
||
href="../_static/opensearch.xml"/>
|
||
<link rel="author" title="关于这些文档" href="../about.html" />
|
||
<link rel="index" title="索引" href="../genindex.html" />
|
||
<link rel="search" title="搜索" href="../search.html" />
|
||
<link rel="copyright" title="版权所有" href="../copyright.html" />
|
||
<link rel="next" title="pprint --- 数据美化输出" href="pprint.html" />
|
||
<link rel="prev" title="types --- 动态类型创建和内置类型名称" href="types.html" />
|
||
<link rel="canonical" href="https://docs.python.org/3/library/copy.html" />
|
||
|
||
|
||
|
||
|
||
|
||
<style>
|
||
@media only screen {
|
||
table.full-width-table {
|
||
width: 100%;
|
||
}
|
||
}
|
||
</style>
|
||
<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>
|
||
|
||
</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" />
|
||
<label for="menuToggler" class="toggler__label">
|
||
<span></span>
|
||
</label>
|
||
<nav class="nav-content" role="navigation">
|
||
<a href="https://www.python.org/" class="nav-logo">
|
||
<img src="../_static/py.svg" alt="Logo"/>
|
||
</a>
|
||
<div class="version_switcher_placeholder"></div>
|
||
<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"
|
||
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" fill="#444"></path>
|
||
</svg>
|
||
<input type="text" name="q" aria-label="快速搜索"/>
|
||
<input type="submit" value="转向"/>
|
||
</form>
|
||
</nav>
|
||
<div class="menu-wrapper">
|
||
<nav class="menu" role="navigation" aria-label="main navigation">
|
||
<div class="language_switcher_placeholder"></div>
|
||
<h4>上一个主题</h4>
|
||
<p class="topless"><a href="types.html"
|
||
title="上一章"><code class="xref py py-mod docutils literal notranslate"><span class="pre">types</span></code> --- 动态类型创建和内置类型名称</a></p>
|
||
<h4>下一个主题</h4>
|
||
<p class="topless"><a href="pprint.html"
|
||
title="下一章"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pprint</span></code> --- 数据美化输出</a></p>
|
||
<div role="note" aria-label="source link">
|
||
<h3>本页</h3>
|
||
<ul class="this-page-menu">
|
||
<li><a href="../bugs.html">报告 Bug</a></li>
|
||
<li>
|
||
<a href="https://github.com/python/cpython/blob/3.8/Doc/library/copy.rst"
|
||
rel="nofollow">显示源代码
|
||
</a>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</nav>
|
||
</div>
|
||
</div>
|
||
|
||
<div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;">
|
||
这个文档所针对的是一个已不再受支持的 Python 旧版本。
|
||
你应当升级版本，并阅读
|
||
<a href="/3/library/copy.html"> Python 当前稳定版本的文档</a>.
|
||
</div>
|
||
|
||
<div class="related" role="navigation" aria-label="related navigation">
|
||
<h3>导航</h3>
|
||
<ul>
|
||
<li class="right" style="margin-right: 10px">
|
||
<a href="../genindex.html" title="总目录"
|
||
accesskey="I">索引</a></li>
|
||
<li class="right" >
|
||
<a href="../py-modindex.html" title="Python 模块索引"
|
||
>模块</a> |</li>
|
||
<li class="right" >
|
||
<a href="pprint.html" title="pprint --- 数据美化输出"
|
||
accesskey="N">下一页</a> |</li>
|
||
<li class="right" >
|
||
<a href="types.html" title="types --- 动态类型创建和内置类型名称"
|
||
accesskey="P">上一页</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">3.8.20 Documentation</a> »
|
||
</li>
|
||
|
||
<li class="nav-item nav-item-1"><a href="index.html" >Python 标准库</a> »</li>
|
||
<li class="nav-item nav-item-2"><a href="datatypes.html" accesskey="U">数据类型</a> »</li>
|
||
<li class="right">
|
||
|
||
|
||
<div class="inline-search" role="search">
|
||
<form class="inline-search" action="../search.html" method="get">
|
||
<input placeholder="快速搜索" aria-label="快速搜索" type="text" name="q" />
|
||
<input type="submit" value="转向" />
|
||
<input type="hidden" name="check_keywords" value="yes" />
|
||
<input type="hidden" name="area" value="default" />
|
||
</form>
|
||
</div>
|
||
|
|
||
</li>
|
||
|
||
</ul>
|
||
</div>
|
||
|
||
<div class="document">
|
||
<div class="documentwrapper">
|
||
<div class="bodywrapper">
|
||
<div class="body" role="main">
|
||
|
||
<section id="module-copy">
|
||
<span id="copy-shallow-and-deep-copy-operations"></span><h1><a class="reference internal" href="#module-copy" title="copy: Shallow and deep copy operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">copy</span></code></a> --- 浅层 (shallow) 和深层 (deep) 复制操作<a class="headerlink" href="#module-copy" title="永久链接至标题">¶</a></h1>
|
||
<p><strong>源代码:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/copy.py">Lib/copy.py</a></p>
|
||
<hr class="docutils" />
|
||
<p>Python 的赋值语句不复制对象，而是创建目标和对象的绑定关系。对于自身可变，或包含可变项的集合，有时要生成副本用于改变操作，而不必改变原始对象。本模块提供了通用的浅层复制和深层复制操作，（如下所述）。</p>
|
||
<p>接口摘要：</p>
|
||
<dl class="function">
|
||
<dt id="copy.copy">
|
||
<code class="sig-prename descclassname">copy.</code><code class="sig-name descname">copy</code><span class="sig-paren">(</span><em class="sig-param">x</em><span class="sig-paren">)</span><a class="headerlink" href="#copy.copy" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>返回 <em>x</em> 的浅复制。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="copy.deepcopy">
|
||
<code class="sig-prename descclassname">copy.</code><code class="sig-name descname">deepcopy</code><span class="sig-paren">(</span><em class="sig-param">x</em><span class="optional">[</span>, <em class="sig-param">memo</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#copy.deepcopy" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>返回 <em>x</em> 的深复制。</p>
|
||
</dd></dl>
|
||
|
||
<dl class="exception">
|
||
<dt id="copy.Error">
|
||
<em class="property">exception </em><code class="sig-prename descclassname">copy.</code><code class="sig-name descname">Error</code><a class="headerlink" href="#copy.Error" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>针对模块特定错误引发。</p>
|
||
</dd></dl>
|
||
|
||
<p id="shallow-vs-deep-copy">浅层与深层复制的区别仅与复合对象（即包含列表或类的实例等其他对象的对象）相关：</p>
|
||
<ul class="simple">
|
||
<li><p><em>浅层复制</em> 构造一个新的复合对象，然后（在尽可能的范围内）将原始对象中找到的对象的 <em>引用</em> 插入其中。</p></li>
|
||
<li><p><em>深层复制</em> 构造一个新的复合对象，然后，递归地将在原始对象里找到的对象的 <em>副本</em> 插入其中。</p></li>
|
||
</ul>
|
||
<p>深度复制操作通常存在两个问题, 而浅层复制操作并不存在这些问题：</p>
|
||
<ul class="simple">
|
||
<li><p>递归对象 (直接或间接包含对自身引用的复合对象) 可能会导致递归循环。</p></li>
|
||
<li><p>由于深层复制会复制所有内容，因此可能会过多复制（例如本应该在副本之间共享的数据）。</p></li>
|
||
</ul>
|
||
<p><a class="reference internal" href="#copy.deepcopy" title="copy.deepcopy"><code class="xref py py-func docutils literal notranslate"><span class="pre">deepcopy()</span></code></a> 函数用以下方式避免了这些问题：</p>
|
||
<ul class="simple">
|
||
<li><p>保留在当前复制过程中已复制的对象的 "备忘录" （<code class="docutils literal notranslate"><span class="pre">memo</span></code>） 字典；以及</p></li>
|
||
<li><p>允许用户定义的类重写复制操作或复制的组件集合。</p></li>
|
||
</ul>
|
||
<p>该模块不复制模块、方法、栈追踪（stack trace）、栈帧（stack frame）、文件、套接字、窗口、数组以及任何类似的类型。它通过不改变地返回原始对象来（浅层或深层地）“复制”函数和类；这与 <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> 模块处理这类问题的方式是相似的。</p>
|
||
<p>制作字典的浅层复制可以使用 <a class="reference internal" href="stdtypes.html#dict.copy" title="dict.copy"><code class="xref py py-meth docutils literal notranslate"><span class="pre">dict.copy()</span></code></a> 方法，而制作列表的浅层复制可以通过赋值整个列表的切片完成，例如，<code class="docutils literal notranslate"><span class="pre">copied_list</span> <span class="pre">=</span> <span class="pre">original_list[:]</span></code>。</p>
|
||
<p id="index-0">类可以使用与控制序列化（pickling）操作相同的接口来控制复制操作，关于这些方法的描述信息请参考 <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> 模块。实际上，<a class="reference internal" href="#module-copy" title="copy: Shallow and deep copy operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">copy</span></code></a> 模块使用的正是从 <a class="reference internal" href="copyreg.html#module-copyreg" title="copyreg: Register pickle support functions."><code class="xref py py-mod docutils literal notranslate"><span class="pre">copyreg</span></code></a> 模块中注册的 pickle 函数。</p>
|
||
<p id="index-1">想要给一个类定义它自己的拷贝操作实现，可以通过定义特殊方法 <code class="xref py py-meth docutils literal notranslate"><span class="pre">__copy__()</span></code> 和 <code class="xref py py-meth docutils literal notranslate"><span class="pre">__deepcopy__()</span></code>。 调用前者以实现浅层拷贝操作，该方法不用传入额外参数。 调用后者以实现深层拷贝操作；它应传入一个参数即 <code class="docutils literal notranslate"><span class="pre">memo</span></code> 字典。 如果 <code class="xref py py-meth docutils literal notranslate"><span class="pre">__deepcopy__()</span></code> 实现需要创建一个组件的深层拷贝，它应当调用 <a class="reference internal" href="#copy.deepcopy" title="copy.deepcopy"><code class="xref py py-func docutils literal notranslate"><span class="pre">deepcopy()</span></code></a> 函数并以该组件作为第一个参数，而将 memo 字典作为第二个参数。</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">参见</p>
|
||
<dl class="simple">
|
||
<dt>模块 <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>讨论了支持对象状态检索和恢复的特殊方法。</p>
|
||
</dd>
|
||
</dl>
|
||
</div>
|
||
</section>
|
||
|
||
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
|
||
<div class="sphinxsidebarwrapper">
|
||
<h4>上一个主题</h4>
|
||
<p class="topless"><a href="types.html"
|
||
title="上一章"><code class="xref py py-mod docutils literal notranslate"><span class="pre">types</span></code> --- 动态类型创建和内置类型名称</a></p>
|
||
<h4>下一个主题</h4>
|
||
<p class="topless"><a href="pprint.html"
|
||
title="下一章"><code class="xref py py-mod docutils literal notranslate"><span class="pre">pprint</span></code> --- 数据美化输出</a></p>
|
||
<div role="note" aria-label="source link">
|
||
<h3>本页</h3>
|
||
<ul class="this-page-menu">
|
||
<li><a href="../bugs.html">报告 Bug</a></li>
|
||
<li>
|
||
<a href="https://github.com/python/cpython/blob/3.8/Doc/library/copy.rst"
|
||
rel="nofollow">显示源代码
|
||
</a>
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
<div class="clearer"></div>
|
||
</div>
|
||
<div class="related" role="navigation" aria-label="related navigation">
|
||
<h3>导航</h3>
|
||
<ul>
|
||
<li class="right" style="margin-right: 10px">
|
||
<a href="../genindex.html" title="总目录"
|
||
>索引</a></li>
|
||
<li class="right" >
|
||
<a href="../py-modindex.html" title="Python 模块索引"
|
||
>模块</a> |</li>
|
||
<li class="right" >
|
||
<a href="pprint.html" title="pprint --- 数据美化输出"
|
||
>下一页</a> |</li>
|
||
<li class="right" >
|
||
<a href="types.html" title="types --- 动态类型创建和内置类型名称"
|
||
>上一页</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">3.8.20 Documentation</a> »
|
||
</li>
|
||
|
||
<li class="nav-item nav-item-1"><a href="index.html" >Python 标准库</a> »</li>
|
||
<li class="nav-item nav-item-2"><a href="datatypes.html" >数据类型</a> »</li>
|
||
<li class="right">
|
||
|
||
|
||
<div class="inline-search" role="search">
|
||
<form class="inline-search" action="../search.html" method="get">
|
||
<input placeholder="快速搜索" aria-label="快速搜索" type="text" name="q" />
|
||
<input type="submit" value="转向" />
|
||
<input type="hidden" name="check_keywords" value="yes" />
|
||
<input type="hidden" name="area" value="default" />
|
||
</form>
|
||
</div>
|
||
|
|
||
</li>
|
||
|
||
</ul>
|
||
</div>
|
||
<div class="footer">
|
||
© <a href="../copyright.html">版权所有</a> 2001-2024, 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 />
|
||
|
||
<br />
|
||
|
||
The Python Software Foundation is a non-profit corporation.
|
||
<a href="https://www.python.org/psf/donations/">Please donate.</a>
|
||
<br />
|
||
<br />
|
||
|
||
最后更新于 12月 09, 2024.
|
||
<a href="https://docs.python.org/3/bugs.html">Found a bug</a>?
|
||
<br />
|
||
|
||
Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 2.4.4.
|
||
</div>
|
||
|
||
</body>
|
||
</html> |