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<!DOCTYPE html>

<html class="no-js" lang="en" >

<head>

<title>16. 附录 — Python tutorial 3.5.2 documentation</title>

</head>

<a href="index.html" class="fa fa-home"> Python tutorial</a>

</form>

</div>

<li class="toctree-l1"><a class="reference internal" href="interpreter.html">2. 使用 Python 解释器</a><ul>

<li class="toctree-l2"><a class="reference internal" href="interpreter.html#tut-invoking">2.1. 调用 Python 解释器</a></li>

<li class="toctree-l2"><a class="reference internal" href="interpreter.html#tut-interp">2.2. 解释器及其环境</a></li>

</ul>

</li>

<li class="toctree-l1"><a class="reference internal" href="introduction.html">3. Python 简介</a><ul>

<li class="toctree-l2"><a class="reference internal" href="introduction.html#tut-calculator">3.1. 将 Python 当做计算器</a></li>

<li class="toctree-l2"><a class="reference internal" href="introduction.html#tut-firststeps">3.2. 编程的第一步</a></li>

</ul>

</li>

<li class="toctree-l1"><a class="reference internal" href="controlflow.html">4. 深入 Python 流程控制</a><ul>

<li class="toctree-l2"><a class="reference internal" href="controlflow.html#range">4.3. range() 函数</a></li>

<li class="toctree-l2"><a class="reference internal" href="controlflow.html#break-continue-else">4.4. break 和 continue 语句, 以及循环中的 else 子句</a></li>

<li class="toctree-l2"><a class="reference internal" href="controlflow.html#tut-defining">4.7. 深入 Python 函数定义</a></li>

</ul>

</li>

<li class="toctree-l2"><a class="reference internal" href="datastructures.html#tut-morelists">5.1. 关于列表更多的内容</a></li>

<li class="toctree-l2"><a class="reference internal" href="datastructures.html#tut-tuples">5.3. 元组和序列</a></li>

<li class="toctree-l2"><a class="reference internal" href="datastructures.html#tut-conditions">5.7. 深入条件控制</a></li>

<li class="toctree-l2"><a class="reference internal" href="datastructures.html#tut-comparing">5.8. 比较序列和其它类型</a></li>

</ul>

</li>

</ul>

</li>

<li class="toctree-l1"><a class="reference internal" href="inputoutput.html">7. 输入和输出</a><ul>

<li class="toctree-l2"><a class="reference internal" href="inputoutput.html#tut-formatting">7.1. 格式化输出</a></li>

</ul>

</li>

<li class="toctree-l1"><a class="reference internal" href="errors.html">8. 错误和异常</a><ul>

<li class="toctree-l2"><a class="reference internal" href="errors.html#tut-userexceptions">8.5. 用户自定义异常</a></li>

<li class="toctree-l2"><a class="reference internal" href="errors.html#tut-cleanup">8.6. 定义清理行为</a></li>

<li class="toctree-l2"><a class="reference internal" href="errors.html#tut-cleanup-with">8.7. 预定义清理行为</a></li>

</ul>

</li>

<li class="toctree-l2"><a class="reference internal" href="classes.html#python">9.2. Python 作用域和命名空间</a></li>

<li class="toctree-l2"><a class="reference internal" href="classes.html#tut-exceptionclasses">9.8. 异常也是类</a></li>

<li class="toctree-l2"><a class="reference internal" href="classes.html#tut-genexps">9.11. 生成器表达式</a></li>

</ul>

</li>

<li class="toctree-l1"><a class="reference internal" href="stdlib.html">10. Python 标准库概览</a><ul>

<li class="toctree-l2"><a class="reference internal" href="stdlib.html#tut-os-interface">10.1. 操作系统接口</a></li>

<li class="toctree-l2"><a class="reference internal" href="stdlib.html#tut-file-wildcards">10.2. 文件通配符</a></li>

<li class="toctree-l2"><a class="reference internal" href="stdlib.html#tut-command-line-arguments">10.3. 命令行参数</a></li>

<li class="toctree-l2"><a class="reference internal" href="stdlib.html#tut-stderr">10.4. 错误输出重定向和程序终止</a></li>

<li class="toctree-l2"><a class="reference internal" href="stdlib.html#tut-string-pattern-matching">10.5. 字符串正则匹配</a></li>

<li class="toctree-l2"><a class="reference internal" href="stdlib.html#tut-internet-access">10.7. 互联网访问</a></li>

<li class="toctree-l2"><a class="reference internal" href="stdlib.html#tut-dates-and-times">10.8. 日期和时间</a></li>

</ul>

</li>

<li class="toctree-l1"><a class="reference internal" href="stdlib2.html">11. 标准库浏览 – Part II</a><ul>

<li class="toctree-l2"><a class="reference internal" href="stdlib2.html#tut-binary-formats">11.3. 使用二进制数据记录布局</a></li>

<li class="toctree-l2"><a class="reference internal" href="stdlib2.html#tut-decimal-fp">11.8. 十进制浮点数算法</a></li>

</ul>

</li>

<li class="toctree-l1"><a class="reference internal" href="venv.html">12. 虚拟环境和包</a><ul>

<li class="toctree-l2"><a class="reference internal" href="venv.html#id4">12.2. 创建虚拟环境</a></li>

</ul>

</li>

<li class="toctree-l1"><a class="reference internal" href="interactive.html">14. 交互式输入行编辑历史回溯</a><ul>

<li class="toctree-l2"><a class="reference internal" href="interactive.html#tab">14.1. Tab 补全和历史记录</a></li>

<li class="toctree-l2"><a class="reference internal" href="interactive.html#tut-commentary">14.2. 其它交互式解释器</a></li>

</ul>

</li>

<li class="toctree-l1"><a class="reference internal" href="floatingpoint.html">15. 浮点数算法：争议和限制</a><ul>

</ul>

</li>

</ul>

</li>

</ul>

</div>

</nav>

<a href="index.html">Python tutorial</a>

</nav>

<a href="_sources/appendix.txt" rel="nofollow"> View page source</a>

</li>

</ul>

<hr/>

</div>

<p>当错误发生时，解释器打印一个错误信息和堆栈跟踪。在交互模式下，它返回主提示符；当输入来自文件的时候，在打印堆栈跟踪后以非零退出状态退出。（在 <a class="reference external" href="https://docs.python.org/3/reference/compound_stmts.html#try">try</a> 声明中被 <a class="reference external" href="https://docs.python.org/3/reference/compound_stmts.html#except">except</a> 子句捕捉到的异常在这种情况下不是错误。）有些错误是非常致命的会导致一个非零状态的退出；这也适用于内部错误以及某些情况的内存耗尽。所有的错误信息都写入到标准错误流；来自执行的命令的普通输出写入到标准输出。</p>

<p>输入中断符（通常是 Control-C 或者 DEL）到主或者从提示符中慧取消输入并且返回到主提示。<a class="footnote-reference" href="#id8" id="id4">[1]</a> 当命令执行中输入中断符会引起 <a class="reference external" href="https://docs.python.org/3/library/exceptions.html#KeyboardInterrupt">KeyboardInterrupt</a> 异常，这个异常能够被一个 <a class="reference external" href="https://docs.python.org/3/reference/compound_stmts.html#try">try</a> 声明处理。</p>

</div>

<span id="tut-scripts"></span><h3>16.1.2. 可执行 Python 脚本<a class="headerlink" href="#python" title="Permalink to this headline">¶</a></h3>

<p>在 BSD’ish Unix 系统上，Python 脚本可直接执行，像 shell 脚本一样，只需要把下面内容加入到</p>

<div class="highlight-default"><div class="highlight"><pre><span></span><span class="ch">#!/usr/bin/env python3.5</span>

</pre></div>

</div>

<p>（假设 python 解释器在用户的 <span class="target" id="index-0"></span><code class="xref std std-envvar docutils literal"><span class="pre">PATH</span></code> 中）脚本的开头，并给予该文件的可执行模式。<code class="docutils literal"><span class="pre">#!</span></code> 必须是文件的头两个字符。在一些系统上，第一行必须以 Unix-style 的行结束符（<code class="docutils literal"><span class="pre">'\n'</span></code>）结束，不能以 Windows 的行结束符（<code class="docutils literal"><span class="pre">'\r\n'</span></code>）。注意 <code class="docutils literal"><span class="pre">'#'</span></code> 在 Python 中是用于注释的。</p>

<p>使用 <strong class="program">chmod</strong> 命令能够给予脚本执行模式或者权限。</p>

<div class="highlight-bash"><div class="highlight"><pre><span></span>$ chmod +x myscript.py

</pre></div>

</div>

<p>在 Windows 系统上，没有一个 “可执行模式” 的概念。Python 安装器会自动地把 <code class="docutils literal"><span class="pre">.py</span></code> 文件和 <code class="docutils literal"><span class="pre">python.exe</span></code> 关联起来，因此双击 Python 分拣将会把它当成一个脚本运行。文件扩展名也可以是 <code class="docutils literal"><span class="pre">.pyw</span></code>，在这种情况下，运行时不会出现控制台窗口。</p>

</div>

<span id="id6"></span><h3>16.1.3. 交互式启动文件<a class="headerlink" href="#tut-startup" title="Permalink to this headline">¶</a></h3>

<p>当你使用交互式 Python 的时候，它常常很方便地执行一些命令在每次解释器启动时。你可以这样做：设置一个名为 <a class="reference external" href="https://docs.python.org/3/using/cmdline.html#envvar-PYTHONSTARTUP">PYTHONSTARTUP</a> 的环境变量为包含你的启动命令的文件名。这跟 Unix shells 的 <code class="file docutils literal"><span class="pre">.profile</span></code> 特点有些类似。</p>

<p>这个文件在交互式会话中是只读的，在当 Python 从脚本中读取命令，以及在当 <code class="file docutils literal"><span class="pre">/dev/tty</span></code> 被作为明确的命令源的时候不只是可读的。该文件在交互式命令被执行的时候在相同的命名空间中能够被执行，因此在交互式会话中定义或者导入的对象能够无需授权就能使用。你也能在文件中更改提示 <code class="docutils literal"><span class="pre">sys.ps1</span></code> 和 <code class="docutils literal"><span class="pre">sys.ps2</span></code>。</p>

<p>如果你想要从当前目录中读取一个附加的启动文件，你可以在全局启动文件中编写代码像这样：<code class="docutils literal"><span class="pre">if</span>

<span class="pre">os.path.isfile('.pythonrc.py'):</span> <span class="pre">exec(open('.pythonrc.py').read())</span></code>。如果你想要在脚本中使用启动文件的话，你必须在脚本中明确要这么做:</p>

<div class="highlight-default"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">os</span>

<span class="n">filename</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">environ</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s1">'PYTHONSTARTUP'</span><span class="p">)</span>

<span class="k">if</span> <span class="n">filename</span> <span class="ow">and</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">isfile</span><span class="p">(</span><span class="n">filename</span><span class="p">):</span>

<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span> <span class="k">as</span> <span class="n">fobj</span><span class="p">:</span>

<span class="n">startup_file</span> <span class="o">=</span> <span class="n">fobj</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>

<span class="n">exec</span><span class="p">(</span><span class="n">startup_file</span><span class="p">)</span>

</pre></div>

</div>

<p>Python 提供两个钩子为了让你们定制 <code class="xref py py-mod docutils literal"><span class="pre">sitecustomize</span></code> 和 <code class="xref py py-mod docutils literal"><span class="pre">usercustomize</span></code>。为了看看它的工作机制的话，你必须首先找到你的用户 site-packages 目录的位置。启动 Python 并且运行这段代码:</p>

<div class="highlight-default"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">site</span>

<span class="gp">>>> </span><span class="n">site</span><span class="o">.</span><span class="n">getusersitepackages</span><span class="p">()</span>

<span class="go">'/home/user/.local/lib/python3.4/site-packages'</span>

</pre></div>

</div>

<p>现在你可以创建一个名为 <code class="file docutils literal"><span class="pre">usercustomize.py</span></code> 的文件在你的用户 site-packages 目录，并且在里面放置你想要的任何内容。它会影响 Python 的每一次调用，除非它以 <a class="reference external" href="https://docs.python.org/3/using/cmdline.html#cmdoption-s">-s</a> （禁用自动导入）选项启动。</p>

<p><code class="xref py py-mod docutils literal"><span class="pre">sitecustomize</span></code> 以同样地方式工作，但是通常由是机器的管理员创建在全局的 site-packages 目录中，并且是在 <code class="xref py py-mod docutils literal"><span class="pre">usercustomize</span></code> 之前导入。请参阅 <a class="reference external" href="https://docs.python.org/3/library/site.html#module-site">site</a> 模块获取更多信息。</p>

<p class="rubric">Footnotes</p>

<tr><td class="label"><a class="fn-backref" href="#id4">[1]</a></td><td>GNU 的 Readline 包的问题可能会阻止这种做法。</td></tr>

</tbody>

</table>

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