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<!DOCTYPE html>
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<title>Python数组复制的陷阱</title>
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title="Permalink to Python数组复制的陷阱">Python数组复制的陷阱</a></h1>
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<abbr class="published" title="2019-06-04T00:00:00+02:00">
Published: Tue 04 June 2019
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By <a class="url fn" href="https://sillyemperor.github.io/author/wang-jiang.html">Wang Jiang</a>
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<p>In <a href="https://sillyemperor.github.io/category/python.html">Python</a>.</p>
<p>tags: <a href="https://sillyemperor.github.io/tag/python.html">Python</a> </p>
</footer><!-- /.post-info --> <p>说是陷阱其实有点标题党，其实是最近的一次DEBUG结果。先看代码：</p>
<blockquote>
<blockquote>
<p>a=[1]*5</p>
</blockquote>
</blockquote>
<p>[1,1,1,1,1]</p>
<blockquote>
<blockquote>
<p>a[0]=2</p>
</blockquote>
</blockquote>
<p>[2,1,1,1,1]</p>
<p>这段代码的含义是复制了5个‘1’作为数组，修改其中一个元素后的结果。没毛病。但是：</p>
<blockquote>
<blockquote>
<p>b=[[1]<em>2]</em>2</p>
</blockquote>
</blockquote>
<p>[[1,1],[1,1]]</p>
<blockquote>
<blockquote>
<p>b[0][0]=2</p>
</blockquote>
</blockquote>
<p>[[2,1],[2,1]]</p>
<p>WTF！这显然不是我们想要的结果。其实问题也很简单，[object]*n=[object,object,...object]，也就是说复制的是对象的引用而不是值复制。例如：</p>
<blockquote>
<blockquote>
<p>o=object()</p>
<p>[o]*2</p>
</blockquote>
</blockquote>
<p>[<object object at 0x1083a7090>, <object object at 0x1083a7090>]</p>
<p>可以看到，其实是同一个对象。</p>
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