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<h2 id="条件语句">条件语句<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#条件语句" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h2>
<p>Python 中的条件语句是通过一条或多条语句的执行结果（即 True 或 False）来决定执行的代码块。</p>
<p>判断的值可以分为：</p>
<ul>
<li>假值 ：None、空列表、空集合、空字典，空元组、空字符串、0、False 等。</li>
<li>真值 ：非空列表、非空集合、非空字典，非空元组、非空字符串、非 0 数值、True 等。</li>
</ul>
<h3 id="if">If<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#if" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p>在 Python 中，要构造分支结构可以使用 <code>if</code>、<code>elif</code> 和 <code>else</code> 关键字。<code>elif</code> 和 <code>else</code> 都是可选的，可以根据需要进行使用。</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 示例</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">>>></span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> int</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">input</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Please enter an integer: &quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">))</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">Please enter an integer: </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">42</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">>>></span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&lt;</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'Negative changed to zero'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> elif</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'Zero'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> elif</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'Single'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> else</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'More'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span></code></pre></figure>
<p>当然如果要构造出更多的分支，可以使用 <code>if...elif...else...</code> 结构或者嵌套的 <code>if...else...</code> 结构。</p>
<h3 id="match">Match<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#match" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p>Python 3.10 引入了新的 <code>match</code> 语句，它是模式匹配的一种形式。<code>match</code> 语句接受一个表达式并将它的值与一系列的模式进行比较。 每个模式都关联到一个代码块，当模式与表达式的值匹配时，该代码块将被执行。这在某种程度上类似于其他语言中的 switch 语句。</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">def</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> http_error</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(status):</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> match</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> status:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> case</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 400</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;Bad request&quot;</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> case</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 404</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;Not found&quot;</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> case</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 418</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;I'm a teapot&quot;</span></span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> #&quot;变量名&quot; `_` 被作为 通配符 并必定会匹配成功</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> case</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> _: </span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;Something's wrong with the internet&quot;</span></span></code></pre></figure>
<p>你可以使用 <code>|</code> （“ or ”）在一个模式中组合几个字面值:</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">case</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 401</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 403</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> |</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 404</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;Not allowed&quot;</span></span></code></pre></figure>
<p><em>注意，<code>match</code> 语句和模式匹配的概念是 Python 3.10 中新增的特性，可能在更早版本的 Python 中无法使用。</em></p>
<h2 id="循环语句">循环语句<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#循环语句" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h2>
<h3 id="for">For<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#for" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p>Python 的 for 语句用于遍历任何序列的项目，如列表或字符串。</p>
<p>Python 的 for 语句与 C 或 Pascal 中的不同。<strong>Python 的 for 语句不迭代算术递增数值</strong>（如 Pascal），或是给予用户定义迭代步骤和暂停条件的能力（如 C），而是迭代列表或字符串等任意序列，元素的迭代顺序与在序列中出现的顺序一致。</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;&quot;&quot;</span></span>
<span data-line><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">用for循环实现1~100求和</span></span>
<span data-line><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;&quot;&quot;</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">sum</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">for</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">in</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> range</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">101</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">):</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> sum</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> +=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">sum</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span></code></pre></figure>
<p><strong>内置函数 range() 表示不可变的数字序列，通常用于在 for 循环中循环指定的次数。</strong></p>
<p>在 Python 中，<code>range()</code> 是一个内置函数，用于生成一个不可变的数字序列。通常，这个函数在 for 循环中使用，用于指定循环的次数。<code>range(101)</code> 可以用来生成一个包含 0 到 100（不包含 101）的整数序列。</p>
<p>你也可以根据需要更改 <code>range()</code> 函数的参数，例如：</p>
<ul>
<li><code>range(1, 101)</code>：生成一个包含 1 到 100（不包含 101）的整数序列。</li>
<li><code>range(1, 101, 2)</code>：生成一个包含 1 到 100 的奇数序列，其中 2 是步长。</li>
<li><code>range(100, 0, -2)</code>：生成一个包含 100 到 1 的偶数序列，其中 -2 是步长。</li>
</ul>
<h3 id="while">While<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#while" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p><code>while</code> 循环语句用于在条件满足的情况下重复执行一个代码块。条件表达式的结果为 <code>True</code> 时，继续循环；结果为 <code>False</code> 时，结束循环。</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;&quot;&quot;</span></span>
<span data-line><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">猜数字游戏</span></span>
<span data-line><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;&quot;&quot;</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">import</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> random</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">answer </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> random.randint(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">100</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">counter </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">while</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> True</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> counter </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">+=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> int</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">input</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'请输入: '</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">))</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&lt;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> answer:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'大一点'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> elif</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> number </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">></span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> answer:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'小一点'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> else</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'恭喜你猜对了!'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> break</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'你总共猜了</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">%d</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">次'</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> %</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> counter)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> counter </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">></span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 7</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'你的智商余额明显不足'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span></code></pre></figure>
<h3 id="break">Break<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#break" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p><code>break</code> 语句可以提前退出循环。具体来说，<strong><code>break</code> 用于完全结束一个循环，并跳出该循环体。</strong></p>
<h3 id="continue">Continue<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#continue" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p><code>continue</code> 语句用于<strong>跳过当前循环的剩余语句，然后继续进行下一轮循环。</strong></p>
<h3 id="else">Else<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#else" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p>在 Python 中，<code>else</code> 子句可以与 <code>for</code> 循环和 <code>while</code> 循环一起使用。当循环正常完成（即没有碰到 <code>break</code> 语句）时，<code>else</code> 块的内容会被执行。这个特性在很多其他语言中都没有，因此对于初学者来说可能会感到有些不熟悉。</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 使用 else 的 for 循环的示例</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">for</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> i </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">in</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> range</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">):</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> i </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 10</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> break</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">else</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;循环正常完成&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span></code></pre></figure>
<p>在这个示例中，循环会正常完成，因为没有任何一个元素使得 <code>i == 10</code> 为 <code>True</code>，所以 <code>break</code> 语句不会被执行，<code>else</code> 块的内容会被打印出来。</p>
<p>如果我们修改 <code>if</code> 语句的条件使得 <code>break</code> 语句被执行，那么 <code>else</code> 块的内容就不会被打印出来：</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="Python" data-theme="github-light github-dark"><code data-language="Python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span>for i in range(5):</span></span>
<span data-line><span> if i == 3:</span></span>
<span data-line><span> break</span></span>
<span data-line><span>else:</span></span>
<span data-line><span> print(&quot;循环正常完成&quot;)</span></span></code></pre></figure>
<p>在这个示例中，当 <code>i</code> 等于 3 时，<code>break</code> 语句就会被执行，所以循环没有正常完成，<code>else</code> 块的内容不会被打印出来。</p>
<p>同样的，<code>else</code> 也可以与 <code>while</code> 循环一起使用，当 <code>while</code> 循环的条件变为 <code>False</code> 时，<code>else</code> 块的内容会被执行。</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">i </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 0</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">while</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> i </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">&lt;</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 5</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> i </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 3</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> break</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> i </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">+=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">else</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;循环正常完成&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span></code></pre></figure>
<p>在这个示例中，当 <code>i</code> 等于 3 时，<code>break</code> 语句就会被执行，所以循环没有正常完成，<code>else</code> 块的内容不会被打印出来。</p>
<h2 id="异常语句">异常语句<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#异常语句" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h2>
<h3 id="tryexceptfinally">try、except、finally<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#tryexceptfinally" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<pre><code class="mermaid">graph TD
A(开始)
B[try 块]
C[except 块1]
D[except 块2]
E[else 块]
F[finally 块]
G(结束)
A --> B
B -- 异常1 --> C
B -- 异常2 --> D
B -- 无异常 --> E
C --> F
D --> F
E --> F
F --> G
</code></pre>
<ol>
<li><strong>确定需要的异常处理结构</strong>：在开始编写异常处理结构时，首先确定你需要 <code>try</code>, <code>except</code>, <code>else</code> 和/或 <code>finally</code> 语句块。要记住的是，<code>except</code> 和 <code>finally</code> 块至少需要一个，否则 <code>try</code> 将失去其意义。</li>
<li><strong>编写 <code>try</code> 语句块</strong>：将可能抛出异常的代码放入 <code>try</code> 块。如果在 <code>try</code> 块中发生异常，Python 将停止执行 <code>try</code> 块的其余部分，并转到 <code>except</code> 块。</li>
<li><strong>编写 <code>except</code> 语句块</strong>：为每种可能抛出的异常类型编写一个 <code>except</code> 块。Python 会按照它们在代码中出现的顺序来检查这些 <code>except</code> 块。如果匹配到异常，Python 将执行相应的 <code>except</code> 块并停止查找。</li>
<li><strong>处理多个异常</strong>：你可以将多个异常类型放入一个元组中，然后使用一个 <code>except</code> 块来处理它们。例如：<code>except (TypeError, ValueError):</code>。</li>
<li><strong>处理所有异常</strong>：如果 <code>except</code> 块后面没有指定异常类型，那么这个 <code>except</code> 块将处理所有异常。你可以通过 <code>logging</code> 或 <code>sys</code> 模块获取异常的详细信息。</li>
<li><strong>重新抛出异常</strong>：如果你在 <code>except</code> 块中捕获了一个异常，然后想要再次抛出它，你可以使用 <code>raise</code> 语句而不需要附加任何参数或信息。</li>
<li><strong>编写 <code>else</code> 语句块</strong>：<code>else</code> 块中的代码只有在 <code>try</code> 块没有发生任何异常时才会被执行。</li>
<li><strong>编写 <code>finally</code> 语句块</strong>：无论是否发生异常，<code>finally</code> 块中的代码总是会被执行。这对于清理（例如关闭文件或网络连接）非常有用。</li>
<li><strong>重构代码</strong>：考虑使用 <code>with</code> 语句或 <code>getattr()</code> 方法等内置的异常处理语句，而不是 <code>try/except</code>。此外，如果可能，尽量避免在同一个 <code>except</code> 块中捕获和抛出相同的异常。最后，除非你确定需要处理所有可能的异常，否则不应该捕获所有异常，因为这可能会隐藏严重的问题。</li>
</ol>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 示例</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">try</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> # 这里可能会抛出异常的代码</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> do_something()</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">except</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> SomeException </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">as</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> e:</span></span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> # 当捕获到SomeException时的处理代码</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> handle_exception(e)</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 实例</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">def</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> div</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(a, b):</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> try</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(a </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">/</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> b)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> except</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> ZeroDivisionError</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;错误：b 不应为 0 !!&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> except</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> Exception</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> as</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> e:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;意外错误：</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">{}</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">.format(e))</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> else</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'只有当一切正常时，才会运行 else'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> finally</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'始终运行 finally 块。'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 测试</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">div(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">div(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'错误的类型'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">div(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line> </span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 在一行中捕获多个异常</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">try</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(a </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">/</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> b)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">except</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">ZeroDivisionError</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">TypeError</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">as</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> e:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(e)</span></span>
<span data-line> </span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 当存在 finally 时，except 是可选的</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">try</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> open</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(database)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">finally</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> close(database)</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 捕获所有错误并记录下来</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">try</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> do_work()</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">except</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">: </span></span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> # 从 logging 模块获取详细信息</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> logging.exception(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'捕获到异常!'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> </span></span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> # 从 sys.exc_info() 方法获取详细信息</span></span>
<span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> error_type, error_value, trace_back </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> sys.exc_info()</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(error_value)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> raise</span></span></code></pre></figure>
<h3 id="with">With<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#with" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p>Python 的 with 语句支持通过上下文管理器所定义的运行时上下文这一概念。</p>
<p><code>with</code> 语句是一种处理上下文管理器的语句，上下文管理器通常包含 <code>__enter__</code> 和 <code>__exit__</code> 这两个方法。在 <code>with</code> 语句的代码块被执行前，会首先执行 <code>__enter__</code> 方法，在执行完毕后，会调用 <code>__exit__</code> 方法。这在你需要管理资源，如文件，网络连接或锁定等情况非常有用，因为它可以<strong>保证在任何情况下都会执行必要的清理操作。</strong></p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 在这里，文件已经被关闭，无需再次手动关闭</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">with</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> open</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;file.txt&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;r&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">as</span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;"> file</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> for</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> line </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">in</span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;"> file</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(line)</span></span></code></pre></figure>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 基本思想是 with 所求值的对象必须有一个 enter() 方法，一个 exit() 方法。</span></span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 紧跟 with 后面的语句被求值后，返回对象的 enter() 方法被调用，并将返回值赋值给 as 后面的变量。</span></span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 当 with 的代码块全部被执行完之后，将调用前面返回对象的 exit() 方法。</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> ManagedFile</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> def</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> __init__</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(self, filename):</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> self</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">.filename </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> filename</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> def</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> __enter__</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(self):</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> self</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">.file </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> open</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">self</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">.filename, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">'r'</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> self</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">.file</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> def</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> __exit__</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(self, exc_type, exc_val, exc_tb):</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> self</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">.file:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> self</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">.file.close()</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 使用自定义的上下文管理器</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">with</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> ManagedFile(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;file.txt&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">as</span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;"> file</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">file</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">.read())</span></span></code></pre></figure>
<h3 id="raise">Raise<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#raise" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p><code>raise</code> 语句用于引发特定的异常。你可以定义异常类型并附加一个错误消息：</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">raise</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> ValueError</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;这是一个无效的值！&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span></code></pre></figure>
<p>如果你在 <code>except</code> 块中使用 <code>raise</code> 语句，而不提供任何参数，它将默认重新引发最近的异常。</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">try</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">5</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">/</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">0</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">except</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> ZeroDivisionError</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> as</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> e:</span></span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;发生了一个错误！&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> raise</span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> # 重新引发最近的异常</span></span></code></pre></figure>
<h2 id="其他语句">其他语句<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#其他语句" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h2>
<h3 id="assert">Assert<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#assert" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p><code>assert</code> 语句用于断言某个条件为真，如果条件为假，则会抛出 <code>AssertionError</code> 异常。它常常用于调试代码，确认代码的某些方面满足预期，例如：</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">assert</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 1</span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> # 条件为真，没有问题</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 条件为假，抛出 AssertionError，并附带错误信息</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">assert</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> x </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> 2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;x should be 2 but is actually &quot;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> +</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> str</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(x) </span></span></code></pre></figure>
<p><em>注意，<code>assert</code> 语句在优化模式下（使用 <code>-O</code> 参数启动 Python 时）会被全局禁用。</em></p>
<h3 id="pass">Pass<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#pass" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p><code>pass</code> 语句是 Python 中的空语句，用于在需要语句的地方保持语法的完整性，但是<strong>实际上不做任何事情</strong>。通常，我们使用它作为未完成代码的占位符：</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">def</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> my_function</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">():</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> pass</span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> # </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">TODO</span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">: implement this function</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> MyEmptyClass</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">:</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> pass</span></span></code></pre></figure>
<h3 id="return">Return<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#return" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h3>
<p><code>return</code> 语句用于从函数返回一个值。所有函数都会返回一个值：如果函数执行到结尾而没有遇到 <code>return</code> 语句，它将返回特殊值 <code>None</code>：</p>
<figure data-rehype-pretty-code-figure><pre tabindex="0" data-language="python" data-theme="github-light github-dark"><code data-language="python" data-theme="github-light github-dark" style="display:grid;"><span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">def</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> add</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(a, b):</span></span>
<span data-line><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> a </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">+</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> b</span></span>
<span data-line> </span>
<span data-line><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">print</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(add(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">1</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">2</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">)) </span><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"># 输出：3</span></span></code></pre></figure></article><hr/><div class="page-footer"></div></div><div class="right sidebar"><div class="graph"><h3>关系图谱</h3><div class="graph-outer"><div id="graph-container" data-cfg="{&quot;drag&quot;:true,&quot;zoom&quot;:true,&quot;depth&quot;:1,&quot;scale&quot;:1.1,&quot;repelForce&quot;:0.5,&quot;centerForce&quot;:0.3,&quot;linkDistance&quot;:30,&quot;fontSize&quot;:0.6,&quot;opacityScale&quot;:1,&quot;showTags&quot;:true,&quot;removeTags&quot;:[],&quot;focusOnHover&quot;:false}"></div><button id="global-graph-icon" aria-label="Global Graph"><svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" viewBox="0 0 55 55" fill="currentColor" xml:space="preserve"><path d="M49,0c-3.309,0-6,2.691-6,6c0,1.035,0.263,2.009,0.726,2.86l-9.829,9.829C32.542,17.634,30.846,17,29,17
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