uTools-Manuals/docs/python/copy.html

<div class="body" role="main"><div class="section" id="module-copy"><h1><span class="yiyi-st" id="yiyi-10">8.10. <a class="reference internal" href="#module-copy" title="copy: Shallow and deep copy operations."><code class="xref py py-mod docutils literal"><span class="pre">copy</span></code></a>  - 浅和深复制操作</span></h1><p><span class="yiyi-st" id="yiyi-11"><strong>源代码：</strong> <a class="reference external" href="https://hg.python.org/cpython/file/3.5/Lib/copy.py">Lib/copy.py</a></span></p><p><span class="yiyi-st" id="yiyi-12">Python中的赋值语句不复制对象，它们在目标和对象之间创建绑定。</span><span class="yiyi-st" id="yiyi-13">对于可变的或包含可变项的容器，有时需要一个副本，所以可以改变一个副本而不改变另一个。</span><span class="yiyi-st" id="yiyi-14">此模块提供通用的浅层和深层复制操作（如下所述）。</span></p><p><span class="yiyi-st" id="yiyi-15">接口概要：</span></p><dl class="function"><dt id="copy.copy"><span class="yiyi-st" id="yiyi-16"><code class="descclassname">copy.</code><code class="descname">copy</code><span class="sig-paren">(</span><em>x</em><span class="sig-paren">)</span></span></dt><dd><p><span class="yiyi-st" id="yiyi-17">返回<em>x</em>的浅拷贝。</span></p></dd></dl><dl class="function"><dt id="copy.deepcopy"><span class="yiyi-st" id="yiyi-18"><code class="descclassname">copy.</code><code class="descname">deepcopy</code><span class="sig-paren">(</span><em>x</em><span class="sig-paren">)</span></span></dt><dd><p><span class="yiyi-st" id="yiyi-19">返回<em>x</em>的深度副本。</span></p></dd></dl><dl class="exception"><dt id="copy.error"><span class="yiyi-st" id="yiyi-20"><em class="property">exception </em><code class="descclassname">copy.</code><code class="descname">error</code></span></dt><dd><p><span class="yiyi-st" id="yiyi-21">引发模块特定错误。</span></p></dd></dl><p><span class="yiyi-st" id="yiyi-22">浅层和深层复制之间的区别仅与复合对象（包含其他对象，如列表或类实例的对象）有关：</span></p><ul class="simple"><li><span class="yiyi-st" id="yiyi-23"><em>浅拷贝</em>构建一个新的复合对象，然后（尽可能地）将原始对象中<em>引用</em>插入到新对象中。</span></li><li><span class="yiyi-st" id="yiyi-24"><em>深拷贝</em>构造一个新的复合对象，然后递归地把包含原始对象中找到的对象的<em>副本</em>插入到新对象中。</span></li></ul><p><span class="yiyi-st" id="yiyi-25">对于浅拷贝操作，深拷贝操作通常不存在两个问题：</span></p><ul class="simple"><li><span class="yiyi-st" id="yiyi-26">递归对象（直接或间接包含对自身引用的复合对象）可能导致递归循环。</span></li><li><span class="yiyi-st" id="yiyi-27">因为深拷贝<em>一切</em>它可能拷贝太多，例如甚至应该在拷贝之间共享的管理数据结构。</span></li></ul><p><span class="yiyi-st" id="yiyi-28"><a class="reference internal" href="#copy.deepcopy" title="copy.deepcopy"><code class="xref py py-func docutils literal"><span class="pre">deepcopy()</span></code></a>函数通过以下方式避免了这些问题：</span></p><ul class="simple"><li><span class="yiyi-st" id="yiyi-29">保持在当前复制过程中已经复制的对象的“备忘录”字典；和</span></li><li><span class="yiyi-st" id="yiyi-30">让用户定义的类覆盖复制操作或复制的组件集。</span></li></ul><p><span class="yiyi-st" id="yiyi-31">此模块不复制像模块，方法，堆栈跟踪，堆栈框架，文件，套接字，窗口，数组或任何类似类型的类型。</span><span class="yiyi-st" id="yiyi-32">它通过返回原始对象不变来“复制”函数和类（浅和深）这与由<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"><span class="pre">pickle</span></code></a>模块处理的方式兼容。</span></p><p><span class="yiyi-st" id="yiyi-33">可以使用<a class="reference internal" href="stdtypes.html#dict.copy" title="dict.copy"><code class="xref py py-meth docutils literal"><span class="pre">dict.copy()</span></code></a>和通过分配整个列表的片段来创建字典的浅拷贝，例如，<code class="docutils literal"><span class="pre">copied_list</span> <span class="pre">=</span> <span class="pre">original_list [：]</span></code>。</span></p><p id="index-0"><span class="yiyi-st" id="yiyi-34">类可以使用相同的接口来控制用于控制酸洗的复制。</span><span class="yiyi-st" id="yiyi-35">有关这些方法的信息，请参阅模块<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"><span class="pre">pickle</span></code></a>的描述。</span><span class="yiyi-st" id="yiyi-36">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"><span class="pre">copy</span></code></a>模块使用来自<a class="reference internal" href="copyreg.html#module-copyreg" title="copyreg: Register pickle support functions."><code class="xref py py-mod docutils literal"><span class="pre">copyreg</span></code></a>模块的注册pickle函数。</span></p><p id="index-1"><span class="yiyi-st" id="yiyi-37">为了让一个类定义自己的拷贝实现，它可以定义特殊的方法<code class="xref py py-meth docutils literal"><span class="pre">__copy__()</span></code>和<code class="xref py py-meth docutils literal"><span class="pre">__deepcopy__()</span></code>。</span><span class="yiyi-st" id="yiyi-38">前者被称为实现浅拷贝操作；不会传递额外的参数。</span><span class="yiyi-st" id="yiyi-39">后者被称为实现深拷贝操作；它传递一个参数，备忘录字典。</span><span class="yiyi-st" id="yiyi-40">如果<code class="xref py py-meth docutils literal"><span class="pre">__deepcopy__()</span></code>实现需要创建组件的深拷贝，则应调用<a class="reference internal" href="#copy.deepcopy" title="copy.deepcopy"><code class="xref py py-func docutils literal"><span class="pre">deepcopy()</span></code></a>函数，将组件作为第一个参数，论据。</span></p><div class="admonition seealso"><p class="first admonition-title"><span class="yiyi-st" id="yiyi-41">也可以看看</span></p><dl class="last docutils"><dt><span class="yiyi-st" id="yiyi-42">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"><span class="pre">pickle</span></code></a></span></dt><dd><span class="yiyi-st" id="yiyi-43">讨论用于支持对象状态检索和恢复的特殊方法。</span></dd></dl></div></div></div>