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<div class="tutorial-container" style="max-width: 960px; margin: 80px auto 40px; padding: 0 20px;"><div class="tutorial-sidebar"><h3>目录</h3><a href="0.html">1. 简介</a><a href="1.html">2. Python历史</a><a href="2.html">3. 安装Python</a><a href="3.html">3.1. Python解释器</a><a href="4.html">4. 第一个Python程序</a><a href="5.html">4.1. 使用文本编辑器</a><a href="6.html">4.2. 输入和输出</a><a href="7.html">5. Python基础</a><a href="8.html">5.1. 数据类型和变量</a><a href="9.html">5.2. 字符串和编码</a><a href="10.html">5.3. 使用list和tuple</a><a href="11.html">5.4. 条件判断</a><a href="12.html">5.5. 模式匹配</a><a href="13.html">5.6. 循环</a><a href="14.html">5.7. 使用dict和set</a><a href="15.html">6. 函数</a><a href="16.html">6.1. 调用函数</a><a href="17.html">6.2. 定义函数</a><a href="18.html">6.3. 函数的参数</a><a href="19.html">6.4. 递归函数</a><a href="20.html">7. 高级特性</a><a href="21.html">7.1. 切片</a><a href="22.html">7.2. 迭代</a><a href="23.html">7.3. 列表生成式</a><a href="24.html">7.4. 生成器</a><a href="25.html">7.5. 迭代器</a><a href="26.html">8. 函数式编程</a><a href="27.html">8.1. 高阶函数</a><a href="28.html">8.1.1. map/reduce</a><a href="29.html">8.1.2. filter</a><a href="30.html">8.1.3. sorted</a><a href="31.html">8.2. 返回函数</a><a href="32.html">8.3. 匿名函数</a><a href="33.html">8.4. 装饰器</a><a href="34.html">8.5. 偏函数</a><a href="35.html">9. 模块</a><a href="36.html">9.1. 使用模块</a><a href="37.html">9.2. 安装第三方模块</a><a href="38.html">10. 面向对象编程</a><a href="39.html">10.1. 类和实例</a><a href="40.html">10.2. 访问限制</a><a href="41.html">10.3. 继承和多态</a><a href="42.html">10.4. 获取对象信息</a><a href="43.html">10.5. 实例属性和类属性</a><a href="44.html">11. 面向对象高级编程</a><a href="45.html">11.1. 使用__slots__</a><a href="46.html">11.2. 使用@property</a><a href="47.html">11.3. 多重继承</a><a href="48.html">11.4. 定制类</a><a href="49.html">11.5. 使用枚举类</a><a href="50.html">11.6. 使用元类</a><a href="51.html">12. 错误、调试和测试</a><a href="52.html">12.1. 错误处理</a><a href="53.html">12.2. 调试</a><a href="54.html">12.3. 单元测试</a><a href="55.html">12.4. 文档测试</a><a href="56.html">13. IO编程</a><a href="57.html">13.1. 文件读写</a><a href="58.html">13.2. StringIO和BytesIO</a><a href="59.html">13.3. 操作文件和目录</a><a href="60.html">13.4. 序列化</a><a href="61.html">14. 进程和线程</a><a href="62.html">14.1. 多进程</a><a href="63.html">14.2. 多线程</a><a href="64.html">14.3. ThreadLocal</a><a href="65.html">14.4. 进程 vs. 线程</a><a href="66.html">14.5. 分布式进程</a><a href="67.html">15. 正则表达式</a><a href="68.html">16. 常用内建模块</a><a href="69.html">16.1. datetime</a><a href="70.html">16.2. collections</a><a href="71.html">16.3. argparse</a><a href="72.html">16.4. base64</a><a href="73.html">16.5. struct</a><a href="74.html">16.6. hashlib</a><a href="75.html">16.7. hmac</a><a href="76.html">16.8. itertools</a><a href="77.html">16.9. contextlib</a><a href="78.html">16.10. urllib</a><a href="79.html">16.11. XML</a><a href="80.html">16.12. HTMLParser</a><a href="81.html">16.13. venv</a><a href="82.html">17. 常用第三方模块</a><a href="83.html">17.1. Pillow</a><a href="84.html">17.2. requests</a><a href="85.html">17.3. chardet</a><a href="86.html">17.4. psutil</a><a href="87.html">18. 图形界面</a><a href="88.html">18.1. 海龟绘图</a><a href="89.html">19. 网络编程</a><a href="90.html">19.1. TCP/IP简介</a><a href="91.html">19.2. TCP编程</a><a href="92.html">19.3. UDP编程</a><a href="93.html">20. 电子邮件</a><a href="94.html">20.1. SMTP发送邮件</a><a href="95.html">20.2. POP3收取邮件</a><a href="96.html">21. 访问数据库</a><a href="97.html">21.1. 使用SQLite</a><a href="98.html">21.2. 使用MySQL</a><a href="99.html">21.3. 使用SQLAlchemy</a><a href="100.html">22. Web开发</a><a href="101.html">22.1. HTTP协议简介</a><a href="102.html">22.2. HTML简介</a><a href="103.html">22.3. WSGI接口</a><a href="104.html">22.4. 使用Web框架</a><a href="105.html">22.5. 使用模板</a><a href="106.html">23. 异步IO</a><a href="107.html">23.1. 协程</a><a href="108.html">23.2. 使用asyncio</a><a href="109.html">23.3. 使用aiohttp</a><a href="110.html">24. FAQ</a><a href="111.html">25. 期末总结</a></div><div class="tutorial-content"><h1>5.5. 模式匹配</h1><div class="tutorial-body"><p>如果要针对某个变量匹配若干种情况，可以使用<code>match</code>语句。</p>
<p>例如，某个学生的成绩只能是<code>A</code>、<code>B</code>、<code>C</code>，用<code>if</code>语句编写如下：</p>
<pre class="hljs"><code class="language-python">score = <span class="hljs-string">'B'</span>
<span class="hljs-keyword">if</span> score == <span class="hljs-string">'A'</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'score is A.'</span>)
<span class="hljs-keyword">elif</span> score == <span class="hljs-string">'B'</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'score is B.'</span>)
<span class="hljs-keyword">elif</span> score == <span class="hljs-string">'C'</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'score is C.'</span>)
<span class="hljs-keyword">else</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'invalid score.'</span>)
</code></pre>
<p>如果用<code>match</code>语句改写，则改写如下：</p>
<pre class="hljs"><code class="language-python">score = <span class="hljs-string">'B'</span>
<span class="hljs-keyword">match</span> score:
<span class="hljs-keyword">case</span> <span class="hljs-string">'A'</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'score is A.'</span>)
<span class="hljs-keyword">case</span> <span class="hljs-string">'B'</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'score is B.'</span>)
<span class="hljs-keyword">case</span> <span class="hljs-string">'C'</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'score is C.'</span>)
<span class="hljs-keyword">case</span> _: <span class="hljs-comment"># _表示匹配到其他任何情况</span>
<span class="hljs-built_in">print</span>(<span class="hljs-string">'score is ???.'</span>)
</code></pre>
<p>使用<code>match</code>语句时，我们依次用<code>case xxx</code>匹配，并且可以在最后（且仅能在最后）加一个<code>case _</code>表示“任意值”，代码较<code>if ... elif ... else ...</code>更易读。</p>
<h3>复杂匹配</h3>
<p><code>match</code>语句除了可以匹配简单的单个值外，还可以匹配多个值、匹配一定范围，并且把匹配后的值绑定到变量：</p>
<pre class="hljs"><code class="language-python">age = <span class="hljs-number">15</span>
<span class="hljs-keyword">match</span> age:
<span class="hljs-keyword">case</span> x <span class="hljs-keyword">if</span> x < <span class="hljs-number">10</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">f'< 10 years old: <span class="hljs-subst">{x}</span>'</span>)
<span class="hljs-keyword">case</span> <span class="hljs-number">10</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'10 years old.'</span>)
<span class="hljs-keyword">case</span> <span class="hljs-number">11</span> | <span class="hljs-number">12</span> | <span class="hljs-number">13</span> | <span class="hljs-number">14</span> | <span class="hljs-number">15</span> | <span class="hljs-number">16</span> | <span class="hljs-number">17</span> | <span class="hljs-number">18</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'11~18 years old.'</span>)
<span class="hljs-keyword">case</span> <span class="hljs-number">19</span>:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'19 years old.'</span>)
<span class="hljs-keyword">case</span> _:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'not sure.'</span>)
</code></pre>
<p>在上面这个示例中，第一个<code>case x if x < 10</code>表示当<code>age < 10</code>成立时匹配，且赋值给变量<code>x</code>，第二个<code>case 10</code>仅匹配单个值，第三个<code>case 11|12|...|18</code>能匹配多个值，用<code>|</code>分隔。</p>
<p>可见，<code>match</code>语句的<code>case</code>匹配非常灵活。</p>
<h3>匹配列表</h3>
<p><code>match</code>语句还可以匹配列表，功能非常强大。</p>
<p>我们假设用户输入了一个命令，用<code>args = ['gcc', 'hello.c']</code>存储，下面的代码演示了如何用<code>match</code>匹配来解析这个列表：</p>
<pre class="hljs"><code class="language-python">args = [<span class="hljs-string">'gcc'</span>, <span class="hljs-string">'hello.c'</span>, <span class="hljs-string">'world.c'</span>]
<span class="hljs-comment"># args = ['clean']</span>
<span class="hljs-comment"># args = ['gcc']</span>
<span class="hljs-keyword">match</span> args:
<span class="hljs-comment"># 如果仅出现gcc，报错:</span>
<span class="hljs-keyword">case</span> [<span class="hljs-string">'gcc'</span>]:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'gcc: missing source file(s).'</span>)
<span class="hljs-comment"># 出现gcc，且至少指定了一个文件:</span>
<span class="hljs-keyword">case</span> [<span class="hljs-string">'gcc'</span>, file1, *files]:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'gcc compile: '</span> + file1 + <span class="hljs-string">', '</span> + <span class="hljs-string">', '</span>.join(files))
<span class="hljs-comment"># 仅出现clean:</span>
<span class="hljs-keyword">case</span> [<span class="hljs-string">'clean'</span>]:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'clean'</span>)
<span class="hljs-keyword">case</span> _:
<span class="hljs-built_in">print</span>(<span class="hljs-string">'invalid command.'</span>)
</code></pre>
<p>第一个<code>case ['gcc']</code>表示列表仅有<code>'gcc'</code>一个字符串，没有指定文件名，报错；</p>
<p>第二个<code>case ['gcc', file1, *files]</code>表示列表第一个字符串是<code>'gcc'</code>，第二个字符串绑定到变量<code>file1</code>，后面的任意个字符串绑定到<code>*files</code>（符号<code>*</code>的作用将在<a href="../../function/parameter/index.html">函数的参数</a>中讲解），它实际上表示至少指定一个文件；</p>
<p>第三个<code>case ['clean']</code>表示列表仅有<code>'clean'</code>一个字符串；</p>
<p>最后一个<code>case _</code>表示其他所有情况。</p>
<p>可见，<code>match</code>语句的匹配规则非常灵活，可以写出非常简洁的代码。</p>
<h3>参考源码</h3>
<p><a href="do_match.py">do_match.py</a></p>
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