Repository navigation
Expand file tree
/
Copy path13.html
More file actions
214 lines (204 loc) · 20.2 KB
/
Copy path13.html
File metadata and controls
214 lines (204 loc) · 20.2 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="description" content="CodeClub - 5.6. 循环">
<meta name="author" content="Jackson">
<title>5.6. 循环 - CodeClub</title>
<link rel="icon" type="image/x-icon" href="../../img/logo.png">
<link rel="preconnect" href="https://fonts.googleapis.com">
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
<link href="https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap" rel="stylesheet">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.1/css/all.min.css" crossorigin="anonymous" referrerpolicy="no-referrer" />
<link rel="stylesheet" href="../../css/main.css">
<link rel="stylesheet" href="../../css/dark-mode.css">
<link rel="stylesheet" href="../../css/mobile-optimizations.css">
<link rel="stylesheet" href="../../css/tutorial.css">
<style>
.tutorial-container { max-width: 960px; margin: 70px auto 40px; padding: 0 20px; }
.tutorial-sidebar { position: fixed; top: 70px; left: 20px; width: 260px; max-height: calc(100vh - 90px); overflow-y: auto; background: var(--bg-secondary, #fff); border-radius: 8px; padding: 16px; box-shadow: 0 2px 8px rgba(0,0,0,0.08); }
.tutorial-sidebar h3 { font-size: 16px; margin-bottom: 12px; color: var(--text-primary, #1a1a2e); }
.tutorial-sidebar a { display: block; padding: 6px 10px; color: var(--text-secondary, #666); text-decoration: none; font-size: 14px; border-radius: 4px; }
.tutorial-sidebar a:hover, .tutorial-sidebar a.active { background: var(--primary, #3b82f6); color: #fff; }
.tutorial-sidebar .sub-link { padding-left: 24px; font-size: 13px; }
.tutorial-content { margin-left: 300px; background: var(--bg-secondary, #fff); border-radius: 8px; padding: 32px; box-shadow: 0 2px 8px rgba(0,0,0,0.08); }
.tutorial-content h1 { font-size: 28px; margin-bottom: 20px; color: var(--text-primary, #1a1a2e); border-bottom: 2px solid var(--primary, #3b82f6); padding-bottom: 12px; }
.tutorial-content h2 { font-size: 22px; margin: 24px 0 16px; color: var(--text-primary, #1a1a2e); }
.tutorial-content h3 { font-size: 18px; margin: 20px 0 12px; }
.tutorial-content p { line-height: 1.8; margin: 12px 0; color: var(--text-secondary, #333); }
.tutorial-content pre { background: #1e1e2e; color: #cdd6f4; padding: 16px; border-radius: 8px; overflow-x: auto; margin: 16px 0; }
.tutorial-content code { font-family: 'Fira Code', 'Cascadia Code', monospace; font-size: 14px; }
.tutorial-content p code { background: #f1f5f9; padding: 2px 6px; border-radius: 4px; color: #e83e8c; }
.tutorial-content blockquote { border-left: 4px solid var(--primary, #3b82f6); padding: 12px 20px; margin: 16px 0; background: #f8fafc; border-radius: 0 8px 8px 0; }
.tutorial-content ul, .tutorial-content ol { padding-left: 24px; margin: 12px 0; }
.tutorial-content li { margin: 6px 0; line-height: 1.7; }
.tutorial-content img { max-width: 100%; border-radius: 8px; margin: 16px 0; }
.tutorial-nav { display: flex; justify-content: space-between; margin-top: 32px; padding-top: 20px; border-top: 1px solid var(--border, #e5e7eb); }
.tutorial-nav a { color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500; }
.tutorial-nav a:hover { text-decoration: underline; }
.tutorial-index { max-width: 960px; margin: 70px auto 40px; padding: 0 20px; }
.tutorial-card { background: var(--bg-secondary, #fff); border-radius: 12px; padding: 24px; margin: 16px 0; box-shadow: 0 2px 8px rgba(0,0,0,0.08); transition: transform 0.2s; }
.tutorial-card:hover { transform: translateY(-2px); }
.tutorial-card h3 { margin: 0 0 8px; color: var(--text-primary, #1a1a2e); }
.tutorial-card p { color: var(--text-secondary, #666); margin: 0 0 12px; }
.tutorial-card .badge { display: inline-block; padding: 4px 10px; border-radius: 20px; font-size: 12px; font-weight: 600; margin-right: 8px; }
.badge-python { background: #3b82f6; color: #fff; }
.badge-git { background: #f97316; color: #fff; }
.badge-ai { background: #8b5cf6; color: #fff; }
@media (max-width: 768px) {
.tutorial-sidebar { display: none; }
.tutorial-content { margin-left: 0; }
}
</style>
</head>
<body>
<nav class="navbar">
<div class="navbar-container">
<a class="navbar-brand" href="../../index.html">
<img src="../../img/logo.png" alt="CodeClub" width="32" height="32">
<span>CodeClub</span>
</a>
<button class="mobile-menu-toggle" aria-label="切换导航菜单">
<span></span><span></span><span></span>
</button>
<ul class="navbar-nav">
<li><a class="nav-link" href="../../index.html">首页</a></li>
<li><a class="nav-link" href="../../nav.html">网址导航</a></li>
<li><a class="nav-link" href="../../blog/">博客</a></li>
<li><a class="nav-link" href="../../wiki/index.html" target="_blank">WiKi</a></li>
<li><a class="nav-link active" href="../../tutorials/index.html">教程</a></li>
<li><a class="nav-link" href="../../book.html">图书</a></li>
<li><a class="nav-link" href="../../contact.html">联系我</a></li>
<li><a class="nav-link" href="../../about.html">关于我</a></li>
</ul>
</div>
</nav>
<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>5.6. 循环</h1><div class="tutorial-body"><pre class="hljs"><code class="language-plain">>>> 1 + 2 + 3
6
</code></pre>
<p>要计算1+2+3+...+10，勉强也能写出来。</p>
<p>但是，要计算1+2+3+...+10000，直接写表达式就不可能了。</p>
<p>为了让计算机能计算成千上万次的重复运算，我们就需要循环语句。</p>
<p>Python的循环有两种，一种是for...in循环，依次把list或tuple中的每个元素迭代出来，看例子：</p>
<pre class="hljs"><code class="language-python">names = [<span class="hljs-string">'Michael'</span>, <span class="hljs-string">'Bob'</span>, <span class="hljs-string">'Tracy'</span>]
<span class="hljs-keyword">for</span> name <span class="hljs-keyword">in</span> names:
<span class="hljs-built_in">print</span>(name)
</code></pre>
<p>执行这段代码，会依次打印<code>names</code>的每一个元素：</p>
<pre class="hljs"><code class="language-plain">Michael
Bob
Tracy
</code></pre>
<p>所以<code>for x in ...</code>循环就是把每个元素代入变量<code>x</code>，然后执行缩进块的语句。</p>
<p>再比如我们想计算1-10的整数之和，可以用一个<code>sum</code>变量做累加：</p>
<pre class="hljs"><code class="language-python"><span class="hljs-built_in">sum</span> = <span class="hljs-number">0</span>
<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>, <span class="hljs-number">6</span>, <span class="hljs-number">7</span>, <span class="hljs-number">8</span>, <span class="hljs-number">9</span>, <span class="hljs-number">10</span>]:
<span class="hljs-built_in">sum</span> = <span class="hljs-built_in">sum</span> + x
<span class="hljs-built_in">print</span>(<span class="hljs-built_in">sum</span>)
</code></pre>
<p>如果要计算1-100的整数之和，从1写到100有点困难，幸好Python提供一个<code>range()</code>函数，可以生成一个整数序列，再通过<code>list()</code>函数可以转换为list。比如<code>range(5)</code>生成的序列是从0开始小于5的整数：</p>
<pre class="hljs"><code class="language-plain">>>> list(range(5))
[0, 1, 2, 3, 4]
</code></pre>
<p><code>range(101)</code>就可以生成0-100的整数序列，计算如下：</p>
<pre class="hljs"><code class="language-python"><span class="hljs-built_in">sum</span> = <span class="hljs-number">0</span>
<span class="hljs-keyword">for</span> x <span class="hljs-keyword">in</span> <span class="hljs-built_in">range</span>(<span class="hljs-number">101</span>):
<span class="hljs-built_in">sum</span> = <span class="hljs-built_in">sum</span> + x
<span class="hljs-built_in">print</span>(<span class="hljs-built_in">sum</span>)
</code></pre>
<p>请自行运行上述代码，看看结果是不是当年高斯同学心算出的5050。</p>
<p>第二种循环是while循环，只要条件满足，就不断循环，条件不满足时退出循环。比如我们要计算100以内所有奇数之和，可以用while循环实现：</p>
<pre class="hljs"><code class="language-python"><span class="hljs-built_in">sum</span> = <span class="hljs-number">0</span>
n = <span class="hljs-number">99</span>
<span class="hljs-keyword">while</span> n > <span class="hljs-number">0</span>:
<span class="hljs-built_in">sum</span> = <span class="hljs-built_in">sum</span> + n
n = n - <span class="hljs-number">2</span>
<span class="hljs-built_in">print</span>(<span class="hljs-built_in">sum</span>)
</code></pre>
<p>在循环内部变量<code>n</code>不断自减，直到变为<code>-1</code>时，不再满足while条件，循环退出。</p>
<h3>练习</h3>
<p>请利用循环依次对list中的每个名字打印出<code>Hello, xxx!</code>：</p>
<pre class="hljs"><code class="language-python">L = [<span class="hljs-string">'Bart'</span>, <span class="hljs-string">'Lisa'</span>, <span class="hljs-string">'Adam'</span>]
</code></pre>
<h3>break</h3>
<p>在循环中，<code>break</code>语句可以提前退出循环。例如，本来要循环打印1～100的数字：</p>
<pre class="hljs"><code class="language-python">n = <span class="hljs-number">1</span>
<span class="hljs-keyword">while</span> n <= <span class="hljs-number">100</span>:
<span class="hljs-built_in">print</span>(n)
n = n + <span class="hljs-number">1</span>
<span class="hljs-built_in">print</span>(<span class="hljs-string">'END'</span>)
</code></pre>
<p>上面的代码可以打印出1~100。</p>
<p>如果要提前结束循环，可以用<code>break</code>语句：</p>
<pre class="hljs"><code class="language-python">n = <span class="hljs-number">1</span>
<span class="hljs-keyword">while</span> n <= <span class="hljs-number">100</span>:
<span class="hljs-keyword">if</span> n > <span class="hljs-number">10</span>: <span class="hljs-comment"># 当n = 11时，条件满足，执行break语句</span>
<span class="hljs-keyword">break</span> <span class="hljs-comment"># break语句会结束当前循环</span>
<span class="hljs-built_in">print</span>(n)
n = n + <span class="hljs-number">1</span>
<span class="hljs-built_in">print</span>(<span class="hljs-string">'END'</span>)
</code></pre>
<p>执行上面的代码可以看到，打印出1~10后，紧接着打印<code>END</code>，程序结束。</p>
<p>可见<code>break</code>的作用是提前结束循环。</p>
<h3>continue</h3>
<p>在循环过程中，也可以通过<code>continue</code>语句，跳过当前的这次循环，直接开始下一次循环。</p>
<pre class="hljs"><code class="language-python">n = <span class="hljs-number">0</span>
<span class="hljs-keyword">while</span> n < <span class="hljs-number">10</span>:
n = n + <span class="hljs-number">1</span>
<span class="hljs-built_in">print</span>(n)
</code></pre>
<p>上面的程序可以打印出1～10。但是，如果我们想只打印奇数，可以用<code>continue</code>语句跳过某些循环：</p>
<pre class="hljs"><code class="language-python">n = <span class="hljs-number">0</span>
<span class="hljs-keyword">while</span> n < <span class="hljs-number">10</span>:
n = n + <span class="hljs-number">1</span>
<span class="hljs-keyword">if</span> n % <span class="hljs-number">2</span> == <span class="hljs-number">0</span>: <span class="hljs-comment"># 如果n是偶数，执行continue语句</span>
<span class="hljs-keyword">continue</span> <span class="hljs-comment"># continue语句会直接继续下一轮循环，后续的print()语句不会执行</span>
<span class="hljs-built_in">print</span>(n)
</code></pre>
<p>执行上面的代码可以看到，打印的不再是1～10，而是1，3，5，7，9。</p>
<p>可见<code>continue</code>的作用是提前结束本轮循环，并直接开始下一轮循环。</p>
<h3>参考源码</h3>
<p><a href="do_for.py">do_for.py</a></p>
<p><a href="do_while.py">do_while.py</a></p>
<h3>小结</h3>
<p>循环是让计算机做重复任务的有效的方法。</p>
<p><code>break</code>语句可以在循环过程中直接退出循环，而<code>continue</code>语句可以提前结束本轮循环，并直接开始下一轮循环。这两个语句通常都<em>必须</em>配合<code>if</code>语句使用。</p>
<p><em>要特别注意</em>，不要滥用<code>break</code>和<code>continue</code>语句。<code>break</code>和<code>continue</code>会造成代码执行逻辑分叉过多，容易出错。大多数循环并不需要用到<code>break</code>和<code>continue</code>语句，上面的两个例子，都可以通过改写循环条件或者修改循环逻辑，去掉<code>break</code>和<code>continue</code>语句。</p>
<p>有些时候，如果代码写得有问题，会让程序陷入“死循环”，也就是永远循环下去。这时可以用<code>Ctrl+C</code>退出程序，或者强制结束Python进程。</p>
<p>请试写一个死循环程序。</p>
</div>
<hr class="gsc-border">
<div id="gsi-chapter-prev-next" class="flex flex-row mt-4">
<div id="gsi-chapter-prev" class="basis-1/2 mr-2 text-left">
<a href="/books/python/basic/match/index.html"
onclick="gs_load_chapter('/books/python/basic/match/index.html',true);return false;"
class="inline-block my-2">
<svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="1.5"
stroke="currentColor">
<path stroke-linecap="round" stroke-linejoin="round"
d="M18.75 19.5l-7.5-7.5 7.5-7.5m-6 15L5.25 12l7.5-7.5" />
</svg>
模式匹配
</a>
</div>
<div id="gsi-chapter-next" class="basis-1/2 ml-2 text-right">
<a href="/books/python/basic/dict-set/index.html"
onclick="gs_load_chapter('/books/python/basic/dict-set/index.html',true);return false;"
class="inline-block my-2">
使用dict和set
<svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="1.5"
stroke="currentColor">
<path stroke-linecap="round" stroke-linejoin="round"
d="M11.25 4.5l7.5 7.5-7.5 7.5m-6-15l7.5 7.5-7.5 7.5" />
</svg>
</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="12.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">← 5.5. 模式匹配</a><a href="14.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">5.7. 使用dict和set →</a></div><p style="margin-top: 16px; font-size: 13px; color: var(--text-secondary, #999);">原文：<a href="https://liaoxuefeng.com/books/python/basic/loop/index.html" style="color: var(--primary, #3b82f6);">廖雪峰 - 5.6. 循环</a></p></div></div>
<footer class="footer">
<div class="footer-content">
<p>© 2024 CodeClub. All rights reserved.</p>
</div>
</footer>
<script src="../../js/dark-mode.js"></script>
<script src="../../js/mobile-menu.js"></script>
</body>
</html>