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<p>**在 Python 中，异常是程序运行时发生的错误，它中断了正常的程序流程。**Python 使用异常对象来表示错误。当程序中发生错误时，Python 会创建一个相应的异常对象。若未处理，程序将终止并显示错误信息。</p>
<p>异常处理是一种编程结构，用于捕获和响应程序中的异常。正确处理异常可以提高程序的健壮性和可靠性，预防中断或崩溃。</p>
<p>异常是一种特殊对象，包含错误的详细信息，如类型和发生时的状态。Python 内置了许多标准异常类型，例如 <code>ValueError</code>、<code>TypeError</code>、<code>IndexError</code>，每种类型对应特定错误。</p>
<p>我们**可以通过异常处理机制捕获异常。**处理异常允许我们决定出错时的响应方式，而非直接让程序崩溃。这对构建健壮和稳定的程序至关重要。</p>
<h3 id="异常层次结构">异常层次结构<a aria-hidden="true" tabindex="-1" href="#异常层次结构" class="internal"> §</a></h3>
<pre><code class="mermaid">graph LR
BaseException --> SystemExit
BaseException --> KeyboardInterrupt
BaseException --> GeneratorExit
BaseException --> Exception
Exception --> StopIteration
Exception --> ArithmeticError
ArithmeticError --> FloatingPointError
ArithmeticError --> OverflowError
ArithmeticError --> ZeroDivisionError
Exception --> AssertionError
Exception --> AttributeError
Exception --> EOFError
Exception --> ImportError
Exception --> ModuleNotFoundError
Exception --> LookupError
LookupError --> IndexError
LookupError --> KeyError
Exception --> NameError
NameError --> UnboundLocalError
Exception --> OSError
OSError --> IOError
Exception --> RuntimeError
RuntimeError --> NotImplementedError
RuntimeError --> RecursionError
Exception --> SyntaxError
Exception --> SystemError
Exception --> TypeError
Exception --> ValueError
Exception --> UnicodeError
</code></pre>
<p>**Python 的异常遵循一定的层次结构。**在这个层次结构的顶端是 <code>BaseException</code> 类，它是所有异常的基类。接着是其他一些内置异常，如 <code>SystemExit</code>、<code>KeyboardInterrupt</code> 等，这些通常用于系统退出和用户中断。</p>
<p>紧随其后的是 <code>Exception</code> 类，它是大多数内置可被应用程序捕获的错误的基类。从 <code>Exception</code> 类派生出更具体的异常类，如 <code>StopIteration</code>、<code>ArithmeticError</code>、<code>LookupError</code> 等，这些类又有自己的子类，分别对应特定的错误情况。</p>
<h2 id="基本异常处理try-except-else-finally">基本异常处理（<code>try</code>, <code>except</code>, <code>else</code>, <code>finally</code>）<a aria-hidden="true" tabindex="-1" href="#基本异常处理try-except-else-finally" class="internal"> §</a></h2>
<p>Python 中处理异常的关键字有四个：<code>try</code>、<code>except</code>、<code>finally</code>、<code>else</code>。</p>
<ul>
<li><code>try</code>: 将可能引发异常的代码放在 <code>try</code> 块中。</li>
<li><code>except</code>: 当 <code>try</code> 块中的代码引发异常时，执行 <code>except</code> 块中的代码。可指定要捕获的异常类型。一个 <code>try</code> 块可以跟随多个 <code>except</code> 块，以捕获不同类型的异常。</li>
<li><code>finally</code>: 不论 <code>try</code> 块是否引发异常，都会执行 <code>finally</code> 块。常用于清理操作，如关闭文件。</li>
<li><code>else</code>: 若 <code>try</code> 块中无异常发生，则执行 <code>else</code> 块。<code>else</code> 是可选的。</li>
</ul>
<div data-rehype-pretty-code-fragment><pre style="background-color:var(--shiki-color-background);" tabindex="0" data-language="Python" data-theme="default"><code data-language="Python" data-theme="default"><span data-line><span style="color:var(--shiki-color-text);">try:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> # 可能抛出异常的代码</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> result = 10 / 0</span></span>
<span data-line><span style="color:var(--shiki-color-text);">except ZeroDivisionError:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> # 处理ZeroDivisionError异常的代码</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> print(&quot;Cannot divide by zero!&quot;)</span></span>
<span data-line><span style="color:var(--shiki-color-text);">else:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> # try代码块成功执行后的代码</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> print(&quot;Operation successful.&quot;)</span></span>
<span data-line><span style="color:var(--shiki-color-text);">finally:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> # 无论是否发生异常都会执行的代码</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> print(&quot;This is the finally block.&quot;)</span></span></code></pre></div>
<h2 id="python-内置标准异常">Python 内置标准异常<a aria-hidden="true" tabindex="-1" href="#python-内置标准异常" class="internal"> §</a></h2>
<table><thead><tr><th>异常名</th><th>描述</th></tr></thead><tbody><tr><td><code>BaseException</code></td><td><strong>所有异常的基类</strong></td></tr><tr><td><code>SystemExit</code></td><td>解释器请求退出</td></tr><tr><td><code>KeyboardInterrupt</code></td><td>用户中断执行 (通常是输入^C)</td></tr><tr><td><code>Exception</code></td><td><strong>常规错误的基类</strong></td></tr><tr><td><code>StopIteration</code></td><td>迭代器没有更多的值</td></tr><tr><td><code>GeneratorExit</code></td><td>生成器 (generator) 发生异常来通知退出</td></tr><tr><td><code>SystemError</code></td><td>解释器发现内部错误</td></tr><tr><td><code>SyntaxError</code></td><td>Python 语法错误</td></tr><tr><td><code>IndentationError</code></td><td>缩进错误</td></tr><tr><td><code>TabError</code></td><td>Tab 和空格混用</td></tr><tr><td><code>NameError</code></td><td>未声明/初始化对象 (没有属性)</td></tr><tr><td><code>UnboundLocalError</code></td><td>访问未初始化的本地变量</td></tr><tr><td><code>AttributeError</code></td><td>对象没有这个属性</td></tr><tr><td><code>TypeError</code></td><td>对类型无效的操作</td></tr><tr><td><code>AssertionError</code></td><td>断言语句失败</td></tr><tr><td><code>ImportError</code></td><td>导入模块/对象失败</td></tr><tr><td><code>ModuleNotFoundError</code></td><td>找不到模块</td></tr><tr><td><code>LookupError</code></td><td>无效数据查询的基类</td></tr><tr><td><code>IndexError</code></td><td>序列中没有此索引 (index)</td></tr><tr><td><code>KeyError</code></td><td>映射中没有这个键</td></tr><tr><td><code>ValueError</code></td><td>传入无效的参数</td></tr><tr><td><code>UnicodeError</code></td><td>Unicode 相关的错误</td></tr><tr><td><code>ArithmeticError</code></td><td>数学运算基类</td></tr><tr><td><code>FloatingPointError</code></td><td>浮点计算错误</td></tr><tr><td><code>OverflowError</code></td><td>数值运算超出最大限制</td></tr><tr><td><code>ZeroDivisionError</code></td><td>除 (或取模) 零 (所有数据类型)</td></tr><tr><td><code>EnvironmentError</code></td><td>操作系统错误的基类</td></tr><tr><td><code>IOError</code></td><td>输入/输出操作失败</td></tr><tr><td><code>OSError</code></td><td>操作系统错误</td></tr><tr><td><code>EOFError</code></td><td>没有内建输入,到达 EOF 标记</td></tr><tr><td><code>RuntimeError</code></td><td>一般的运行时错误</td></tr><tr><td><code>NotImplementedError</code></td><td>尚未实现的方法</td></tr><tr><td><code>RecursionError</code></td><td>超过最大递归深度</td></tr></tbody></table>
<h2 id="自定义异常的创建和抛出">自定义异常的创建和抛出<a aria-hidden="true" tabindex="-1" href="#自定义异常的创建和抛出" class="internal"> §</a></h2>
<p>**自定义异常通过继承 <code>Exception</code> 类来定义。**在自定义类中，可以定义所需的任何方法，但通常自定义异常很简单，只提供基本信息。</p>
<p>要抛出自定义异常，使用 <code>raise</code> 关键字。在 <code>raise</code> 语句后，指定异常类型和可选的错误消息。</p>
<div data-rehype-pretty-code-fragment><pre style="background-color:var(--shiki-color-background);" tabindex="0" data-language="Python" data-theme="default"><code data-language="Python" data-theme="default"><span data-line><span style="color:var(--shiki-color-text);">class CustomError(Exception):</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> &quot;&quot;&quot;自定义的异常类型&quot;&quot;&quot;</span></span>
<span data-line><span style="color:var(--shiki-color-text);"></span></span>
<span data-line><span style="color:var(--shiki-color-text);"> def __init__(self, message):</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> self.message = message</span></span>
<span data-line><span style="color:var(--shiki-color-text);"></span></span>
<span data-line><span style="color:var(--shiki-color-text);">try:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> raise CustomError(&quot;This is a custom error.&quot;)</span></span>
<span data-line><span style="color:var(--shiki-color-text);">except CustomError as e:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> print(&quot;Caught an exception:&quot;, e.message)</span></span></code></pre></div>
<h2 id="异常链raise-from和异常上下文">异常链（<code>raise from</code>）和异常上下文<a aria-hidden="true" tabindex="-1" href="#异常链raise-from和异常上下文" class="internal"> §</a></h2>
<p>Python 3 引入异常链允许在处理异常时引发另一个异常，保留原始异常的上下文。使用 <code>raise from</code> 实现。</p>
<div data-rehype-pretty-code-fragment><pre style="background-color:var(--shiki-color-background);" tabindex="0" data-language="python" data-theme="default"><code data-language="python" data-theme="default"><span data-line><span style="color:var(--shiki-token-keyword);">try</span><span style="color:var(--shiki-token-punctuation);">:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-constant);">int</span><span style="color:var(--shiki-token-punctuation);">(</span><span style="color:var(--shiki-token-string-expression);">'a'</span><span style="color:var(--shiki-token-punctuation);">)</span></span>
<span data-line><span style="color:var(--shiki-token-keyword);">except</span><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-constant);">ValueError</span><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-keyword);">as</span><span style="color:var(--shiki-color-text);"> e</span><span style="color:var(--shiki-token-punctuation);">:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-keyword);">raise</span><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-constant);">RuntimeError</span><span style="color:var(--shiki-token-punctuation);">(</span><span style="color:var(--shiki-token-string-expression);">'转换错误'</span><span style="color:var(--shiki-token-punctuation);">)</span><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-keyword);">from</span><span style="color:var(--shiki-color-text);"> e</span></span></code></pre></div>
<h2 id="警告warnings-模块的实用场景">警告（<code>warnings</code> 模块）的实用场景<a aria-hidden="true" tabindex="-1" href="#警告warnings-模块的实用场景" class="internal"> §</a></h2>
<p>警告不中断程序，但提供有关潜在问题的信息。<code>warnings</code> 模块发出警告并处理。使用警告来通知即将废弃的功能，或提醒用户注意非关键问题。</p>
<div data-rehype-pretty-code-fragment><pre style="background-color:var(--shiki-color-background);" tabindex="0" data-language="python" data-theme="default"><code data-language="python" data-theme="default"><span data-line><span style="color:var(--shiki-token-keyword);">import</span><span style="color:var(--shiki-color-text);"> warnings</span></span>
<span data-line> </span>
<span data-line><span style="color:var(--shiki-token-keyword);">def</span><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-function);">my_function</span><span style="color:var(--shiki-color-text);">():</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> warnings</span><span style="color:var(--shiki-token-punctuation);">.</span><span style="color:var(--shiki-token-function);">warn</span><span style="color:var(--shiki-token-punctuation);">(</span><span style="color:var(--shiki-token-string-expression);">&quot;这个功能即将废弃&quot;</span><span style="color:var(--shiki-token-punctuation);">, </span><span style="color:var(--shiki-token-constant);">DeprecationWarning</span><span style="color:var(--shiki-token-punctuation);">)</span></span>
<span data-line> </span>
<span data-line><span style="color:var(--shiki-token-function);">my_function</span><span style="color:var(--shiki-token-punctuation);">()</span></span></code></pre></div>
<h2 id="异常处理最佳实践">异常处理最佳实践<a aria-hidden="true" tabindex="-1" href="#异常处理最佳实践" class="internal"> §</a></h2>
<h3 id="合适的异常处理策略">合适的异常处理策略<a aria-hidden="true" tabindex="-1" href="#合适的异常处理策略" class="internal"> §</a></h3>
<ul>
<li><strong>确切地知道你在捕获什么</strong>：仅捕获能正确处理的异常。</li>
<li><strong>避免捕获太广泛的异常</strong>：避免使用空 <code>except:</code> 子句，以免捕获所有异常。</li>
<li><strong>在正确的层级处理异常</strong>：在适当的抽象级别处理异常，避免在函数内部处理应由调用者处理的异常。</li>
</ul>
<h3 id="避免常见错误">避免常见错误<a aria-hidden="true" tabindex="-1" href="#避免常见错误" class="internal"> §</a></h3>
<ul>
<li><strong>过度使用异常处理</strong>：不要使用异常处理来控制正常程序流程。</li>
<li><strong>在异常处理中隐藏错误</strong>：捕获异常时应记录或报告错误信息。</li>
<li><strong>错误地屏蔽异常</strong>：避免在 <code>except</code> 块中引发新异常，覆盖原始异常。</li>
</ul>
<h2 id="异常处理示例网络应用程序">异常处理示例：网络应用程序<a aria-hidden="true" tabindex="-1" href="#异常处理示例网络应用程序" class="internal"> §</a></h2>
<p>在网络应用程序中，需要从远程服务器获取数据。这可能因多种原因失败，如网络问题或服务器错误。使用异常处理优雅地处理这些问题，并提供回退机制或错误信息。</p>
<div data-rehype-pretty-code-fragment><pre style="background-color:var(--shiki-color-background);" tabindex="0" data-language="python" data-theme="default"><code data-language="python" data-theme="default"><span data-line><span style="color:var(--shiki-token-keyword);">import</span><span style="color:var(--shiki-color-text);"> requests</span></span>
<span data-line> </span>
<span data-line><span style="color:var(--shiki-token-keyword);">try</span><span style="color:var(--shiki-token-punctuation);">:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> response </span><span style="color:var(--shiki-token-keyword);">=</span><span style="color:var(--shiki-color-text);"> requests</span><span style="color:var(--shiki-token-punctuation);">.</span><span style="color:var(--shiki-token-function);">get</span><span style="color:var(--shiki-token-punctuation);">(</span><span style="color:var(--shiki-token-string-expression);">'https://example.com/data'</span><span style="color:var(--shiki-token-punctuation);">)</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> response</span><span style="color:var(--shiki-token-punctuation);">.</span><span style="color:var(--shiki-token-function);">raise_for_status</span><span style="color:var(--shiki-token-punctuation);">()</span></span>
<span data-line><span style="color:var(--shiki-token-keyword);">except</span><span style="color:var(--shiki-color-text);"> requests</span><span style="color:var(--shiki-token-punctuation);">.</span><span style="color:var(--shiki-color-text);">exceptions</span><span style="color:var(--shiki-token-punctuation);">.</span><span style="color:var(--shiki-color-text);">HTTPError </span><span style="color:var(--shiki-token-keyword);">as</span><span style="color:var(--shiki-color-text);"> he</span><span style="color:var(--shiki-token-punctuation);">:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-function);">print</span><span style="color:var(--shiki-token-punctuation);">(</span><span style="color:var(--shiki-token-keyword);">f</span><span style="color:var(--shiki-token-string-expression);">'HTTP错误: </span><span style="color:var(--shiki-token-constant);">{</span><span style="color:var(--shiki-token-punctuation);">he</span><span style="color:var(--shiki-token-constant);">}</span><span style="color:var(--shiki-token-string-expression);">'</span><span style="color:var(--shiki-token-punctuation);">)</span></span>
<span data-line><span style="color:var(--shiki-token-keyword);">except</span><span style="color:var(--shiki-color-text);"> requests</span><span style="color:var(--shiki-token-punctuation);">.</span><span style="color:var(--shiki-color-text);">exceptions</span><span style="color:var(--shiki-token-punctuation);">.</span><span style="color:var(--shiki-color-text);">ConnectionError </span><span style="color:var(--shiki-token-keyword);">as</span><span style="color:var(--shiki-color-text);"> ce</span><span style="color:var(--shiki-token-punctuation);">:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-function);">print</span><span style="color:var(--shiki-token-punctuation);">(</span><span style="color:var(--shiki-token-keyword);">f</span><span style="color:var(--shiki-token-string-expression);">'连接错误: </span><span style="color:var(--shiki-token-constant);">{</span><span style="color:var(--shiki-token-punctuation);">ce</span><span style="color:var(--shiki-token-constant);">}</span><span style="color:var(--shiki-token-string-expression);">'</span><span style="color:var(--shiki-token-punctuation);">)</span></span>
<span data-line><span style="color:var(--shiki-token-keyword);">except</span><span style="color:var(--shiki-color-text);"> requests</span><span style="color:var(--shiki-token-punctuation);">.</span><span style="color:var(--shiki-color-text);">exceptions</span><span style="color:var(--shiki-token-punctuation);">.</span><span style="color:var(--shiki-color-text);">Timeout </span><span style="color:var(--shiki-token-keyword);">as</span><span style="color:var(--shiki-color-text);"> te</span><span style="color:var(--shiki-token-punctuation);">:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-function);">print</span><span style="color:var(--shiki-token-punctuation);">(</span><span style="color:var(--shiki-token-keyword);">f</span><span style="color:var(--shiki-token-string-expression);">'请求超时: </span><span style="color:var(--shiki-token-constant);">{</span><span style="color:var(--shiki-token-punctuation);">te</span><span style="color:var(--shiki-token-constant);">}</span><span style="color:var(--shiki-token-string-expression);">'</span><span style="color:var(--shiki-token-punctuation);">)</span></span>
<span data-line><span style="color:var(--shiki-token-keyword);">else</span><span style="color:var(--shiki-token-punctuation);">:</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-comment);"># 处理成功的响应</span></span>
<span data-line><span style="color:var(--shiki-color-text);"> </span><span style="color:var(--shiki-token-function);">process_data</span><span style="color:var(--shiki-token-punctuation);">(response)</span></span></code></pre></div>
<p>在这个例子中，使用 <a href="../../../../Tech/programming-language/Python/模块/网络处理/requests-HTTP-库" class="internal" data-slug="Tech/programming-language/Python/模块/网络处理/requests-HTTP-库">requests HTTP 库</a> 分别处理了 HTTP 错误、连接错误和超时错误，每种类型的错误都有专门的异常类。这使得错误处理更加具体和有用。</p></article></div><div class="right sidebar"><div class="graph "><h3>Graph View</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;:[]}"></div><svg version="1.1" id="global-graph-icon" xmlns="http://www.w3.org/2000/svg" xmlnsXlink="http://www.w3.org/1999/xlink" x="0px" y="0px" viewBox="0 0 55 55" fill="currentColor" xmlSpace="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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