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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>8.1.3. sorted</h1><div class="tutorial-body"><p>Python内置的<code>sorted()</code>函数就可以对list进行排序：</p>

<pre class="hljs"><code class="language-plain">>>> sorted([36, 5, -12, 9, -21])

[-21, -12, 5, 9, 36]

</code></pre>

<p>此外，<code>sorted()</code>函数也是一个高阶函数，它还可以接收一个<code>key</code>函数来实现自定义的排序，例如按绝对值大小排序：</p>

<pre class="hljs"><code class="language-plain">>>> sorted([36, 5, -12, 9, -21], key=abs)

[5, 9, -12, -21, 36]

</code></pre>

<p>key指定的函数将作用于list的每一个元素上，并根据key函数返回的结果进行排序。对比原始的list和经过<code>key=abs</code>处理过的list：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-built_in">list</span> = [<span class="hljs-number">36</span>, <span class="hljs-number">5</span>, -<span class="hljs-number">12</span>, <span class="hljs-number">9</span>, -<span class="hljs-number">21</span>]

keys = [<span class="hljs-number">36</span>, <span class="hljs-number">5</span>, <span class="hljs-number">12</span>, <span class="hljs-number">9</span>, <span class="hljs-number">21</span>]

</code></pre>

<p>然后<code>sorted()</code>函数按照keys进行排序，并按照对应关系返回list相应的元素：</p>

<pre class="ascii"><code>keys sort => [5, 9, 12, 21, 36]

| | | | |

result sort => [5, 9, -12, -21, 36]

</code></pre>

<p>我们再看一个字符串排序的例子：</p>

<pre class="hljs"><code class="language-plain">>>> sorted(['bob', 'about', 'Zoo', 'Credit'])

['Credit', 'Zoo', 'about', 'bob']

</code></pre>

<p>默认情况下，对字符串排序，是按照ASCII的大小比较的，由于<code>'Z' < 'a'</code>，结果，大写字母<code>Z</code>会排在小写字母<code>a</code>的前面。</p>

<p>现在，我们提出排序应该忽略大小写，按照字母序排序。要实现这个算法，不必对现有代码大加改动，只要我们能用一个key函数把字符串映射为忽略大小写排序即可。忽略大小写来比较两个字符串，实际上就是先把字符串都变成大写（或者都变成小写），再比较。</p>

<p>这样，我们给<code>sorted</code>传入key函数，即可实现忽略大小写的排序：</p>

<pre class="hljs"><code class="language-plain">>>> sorted(['bob', 'about', 'Zoo', 'Credit'], key=str.lower)

['about', 'bob', 'Credit', 'Zoo']

</code></pre>

<p>要进行反向排序，不必改动key函数，可以传入第三个参数<code>reverse=True</code>：</p>

<pre class="hljs"><code class="language-plain">>>> sorted(['bob', 'about', 'Zoo', 'Credit'], key=str.lower, reverse=True)

['Zoo', 'Credit', 'bob', 'about']

</code></pre>

<p>从上述例子可以看出，高阶函数的抽象能力是非常强大的，而且，核心代码可以保持得非常简洁。</p>

<p><code>sorted()</code>也是一个高阶函数。用<code>sorted()</code>排序的关键在于实现一个映射函数。</p>

<p>假设我们用一组tuple表示学生名字和成绩：</p>

<pre class="hljs"><code class="language-python">L = [(<span class="hljs-string">'Bob'</span>, <span class="hljs-number">75</span>), (<span class="hljs-string">'Adam'</span>, <span class="hljs-number">92</span>), (<span class="hljs-string">'Bart'</span>, <span class="hljs-number">66</span>), (<span class="hljs-string">'Lisa'</span>, <span class="hljs-number">88</span>)]

</code></pre>

<p>请用<code>sorted()</code>对上述列表分别按名字排序：</p>

<span class="hljs-keyword">def</span> <span class="hljs-title function_">by_name</span>(<span class="hljs-params">t</span>):

L2 = <span class="hljs-built_in">sorted</span>(L, key=by_name)

<span class="hljs-built_in">print</span>(L2)

</code></pre>

<p>再按成绩从高到低排序：</p>

<span class="hljs-keyword">def</span> <span class="hljs-title function_">by_score</span>(<span class="hljs-params">t</span>):

L2 = <span class="hljs-built_in">sorted</span>(L, key=by_score)

<span class="hljs-built_in">print</span>(L2)

</code></pre>

<p><a href="do_sorted.py">do_sorted.py</a></p>

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filter

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返回函数

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</a></div><div style="display: flex; justify-content: space-between; margin-top: 32px; padding-top: 20px; border-top: 1px solid var(--border, #e5e7eb);"><a href="29.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">← 8.1.2. filter</a><a href="31.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">8.2. 返回函数 →</a></div><p style="margin-top: 16px; font-size: 13px; color: var(--text-secondary, #999);">原文：<a href="https://liaoxuefeng.com/books/python/functional/higher-order-function/sorted/index.html" style="color: var(--primary, #3b82f6);">廖雪峰 - 8.1.3. sorted</a></p></div></div>

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