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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>7.5. 迭代器</h1><div class="tutorial-body"><p>一类是集合数据类型，如<code>list</code>、<code>tuple</code>、<code>dict</code>、<code>set</code>、<code>str</code>等；</p>

<p>一类是<code>generator</code>，包括生成器和带<code>yield</code>的generator function。</p>

<p>这些可以直接作用于<code>for</code>循环的对象统称为可迭代对象：<code>Iterable</code>。</p>

<p>可以使用<code>isinstance()</code>判断一个对象是否是<code>Iterable</code>对象：</p>

<pre class="hljs"><code class="language-plain">>>> from collections.abc import Iterable

>>> isinstance([], Iterable)

True

>>> isinstance({}, Iterable)

True

>>> isinstance('abc', Iterable)

True

>>> isinstance((x for x in range(10)), Iterable)

True

>>> isinstance(100, Iterable)

False

</code></pre>

<p>而生成器不但可以作用于<code>for</code>循环，还可以被<code>next()</code>函数不断调用并返回下一个值，直到最后抛出<code>StopIteration</code>错误表示无法继续返回下一个值了。</p>

<p>可以被<code>next()</code>函数调用并不断返回下一个值的对象称为迭代器：<code>Iterator</code>。</p>

<p>可以使用<code>isinstance()</code>判断一个对象是否是<code>Iterator</code>对象：</p>

<pre class="hljs"><code class="language-plain">>>> from collections.abc import Iterator

>>> isinstance((x for x in range(10)), Iterator)

True

>>> isinstance([], Iterator)

False

>>> isinstance({}, Iterator)

False

>>> isinstance('abc', Iterator)

False

</code></pre>

<p>生成器都是<code>Iterator</code>对象，但<code>list</code>、<code>dict</code>、<code>str</code>虽然是<code>Iterable</code>，却不是<code>Iterator</code>。</p>

<p>把<code>list</code>、<code>dict</code>、<code>str</code>等<code>Iterable</code>变成<code>Iterator</code>可以使用<code>iter()</code>函数：</p>

<pre class="hljs"><code class="language-plain">>>> isinstance(iter([]), Iterator)

True

>>> isinstance(iter('abc'), Iterator)

True

</code></pre>

<p>你可能会问，为什么<code>list</code>、<code>dict</code>、<code>str</code>等数据类型不是<code>Iterator</code>？</p>

<p>这是因为Python的<code>Iterator</code>对象表示的是一个数据流，<code>Iterator</code>对象可以被<code>next()</code>函数调用并不断返回下一个数据，直到没有数据时抛出<code>StopIteration</code>错误。可以把这个数据流看做是一个有序序列，但我们却不能提前知道序列的长度，只能不断通过<code>next()</code>函数实现按需计算下一个数据，所以<code>Iterator</code>的计算是惰性的，只有在需要返回下一个数据时它才会计算。</p>

<p><code>Iterator</code>甚至可以表示一个无限大的数据流，例如全体自然数。而使用list是永远不可能存储全体自然数的。</p>

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

<p>凡是可作用于<code>for</code>循环的对象都是<code>Iterable</code>类型；</p>

<p>凡是可作用于<code>next()</code>函数的对象都是<code>Iterator</code>类型，它们表示一个惰性计算的序列；</p>

<p>集合数据类型如<code>list</code>、<code>dict</code>、<code>str</code>等是<code>Iterable</code>但不是<code>Iterator</code>，不过可以通过<code>iter()</code>函数获得一个<code>Iterator</code>对象。</p>

<p>Python的<code>for</code>循环本质上就是通过不断调用<code>next()</code>函数实现的，例如：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-keyword">for</span> x <span class="hljs-keyword">in</span> [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>]:

</code></pre>

<p>实际上完全等价于：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-comment"># 首先获得Iterator对象:</span>

it = <span class="hljs-built_in">iter</span>([<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">4</span>, <span class="hljs-number">5</span>])

<span class="hljs-keyword">while</span> <span class="hljs-literal">True</span>:

<span class="hljs-keyword">try</span>:

<span class="hljs-comment"># 获得下一个值:</span>

x = <span class="hljs-built_in">next</span>(it)

<span class="hljs-keyword">except</span> StopIteration:

<span class="hljs-comment"># 遇到StopIteration就退出循环</span>

<span class="hljs-keyword">break</span>

</code></pre>

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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="24.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">← 7.4. 生成器</a><a href="26.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">8. 函数式编程 →</a></div><p style="margin-top: 16px; font-size: 13px; color: var(--text-secondary, #999);">原文：<a href="https://liaoxuefeng.com/books/python/advanced/iterator/index.html" style="color: var(--primary, #3b82f6);">廖雪峰 - 7.5. 迭代器</a></p></div></div>

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