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<!DOCTYPE html>
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<li class="toctree-l1"><a class="reference internal" href="appetite.html">1. 开胃菜</a></li>
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<li class="toctree-l2"><a class="reference internal" href="stdlib2.html#tut-output-formatting">11.1. 输出格式</a></li>
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<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>
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<div class="section" id="tut-appendix">
<span id="id1"></span><h1>15. 附录<a class="headerlink" href="#tut-appendix" title="Permalink to this headline">¶</a></h1>
<div class="section" id="tut-interac">
<span id="id2"></span><h2>15.1. 交互模式<a class="headerlink" href="#tut-interac" title="Permalink to this headline">¶</a></h2>
<div class="section" id="tut-error">
<span id="id3"></span><h3>15.1.1. 错误处理<a class="headerlink" href="#tut-error" title="Permalink to this headline">¶</a></h3>
<p>有错误发生时，解释器会打印一个错误信息和栈跟踪器。在交互模式下，它返回主提示符，如果从文件输入执行，它在打印栈跟踪器后以非零状态退出。(异常可以由 <a class="reference external" href="https://docs.python.org/2.7/reference/compound_stmts.html#try">try</a> 语句中的 <a class="reference external" href="https://docs.python.org/2.7/reference/compound_stmts.html#except">except</a> 子句来控制，这样就不会出现上文中的错误信息) 有一些非常致命的错误会导致非零状态下退出，这通常由内部矛盾和内存溢出造成。所有的错误信息都写入标准错误流；命令中执行的普通输出写入标准输出。</p>
<p>在主提示符或从属提示符中输入中断符 (通常是 Control-C 或者 DEL) 就会取消当前输入，回到主命令行。<a class="footnote-reference" href="#id8" id="id4">[1]</a> 执行命令时输入一个中断符会抛出一个 <a class="reference external" href="https://docs.python.org/2.7/library/exceptions.html#exceptions.KeyboardInterrupt">KeyboardInterrupt</a> 异常，它可以被 <a class="reference external" href="https://docs.python.org/2.7/reference/compound_stmts.html#try">try</a> 语句截获。</p>
</div>
<div class="section" id="python">
<span id="tut-scripts"></span><h3>15.1.2. 执行 Python 脚本<a class="headerlink" href="#python" title="Permalink to this headline">¶</a></h3>
<p>BSD 类的 Unix 系统中，Python 脚本可以像 Shell 脚本那样直接执行。只要在脚本文件开头写一行命令，指定文件和模式:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c">#! /usr/bin/env python</span>
</pre></div>
</div>
<p>(首先要确认 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) <code class="docutils literal"><span class="pre">#!</span></code> 必须是文件的前两个字符，在某些平台上，第一行必须以 Unix 风格的行结束符 (<code class="docutils literal"><span class="pre">'\n'</span></code>)结束，不能用 Windows (<code class="docutils literal"><span class="pre">'\r\n'</span></code>) 的结束符。注意，<code class="docutils literal"><span class="pre">'#'</span></code> 是 Python 中是行注释的起始符。</p>
<p>脚本可以通过 <strong class="program">chmod</strong> 命令指定执行模式和权限。</p>
<div class="highlight-bash"><div class="highlight"><pre><span class="nv">$ </span>chmod +x myscript.py
</pre></div>
</div>
<p>Windows 系统上没有“执行模式”。Python 安装程序自动将 <code class="docutils literal"><span class="pre">.py</span></code> 文件关联到 <code class="docutils literal"><span class="pre">python.exe</span></code> ，所以在 Python 文件图标上双击，它就会作为脚本执行。同样 <code class="docutils literal"><span class="pre">.pyw</span></code> 也做了这样的关联，通常它执行时不会显示控制台窗口。</p>
</div>
<div class="section" id="tut-startup">
<span id="id6"></span><h3>15.1.3. 交互执行文件<a class="headerlink" href="#tut-startup" title="Permalink to this headline">¶</a></h3>
<p>使用 Python 解释器的时候，我们可能需要在每次解释器启动时执行一些命令。你可以在一个文件中包含你想要执行的命令，设定一个名为 <a class="reference external" href="https://docs.python.org/2.7/using/cmdline.html#envvar-PYTHONSTARTUP">PYTHONSTARTUP</a> 的环境变量来指定这个文件。这类似于 Unix shell 的 <code class="file docutils literal"><span class="pre">.profile</span></code> 文件。</p>
<p>这个文件在交互会话期是只读的，当 Python 从脚本中解读文件或以终端 <code class="file docutils literal"><span class="pre">/dev/tty</span></code> 做为外部命令源时则不会如此 (尽管它们的行为很像是处在交互会话期) 它与解释器执行的命令处在同一个命名空间，所以由它定义或引用的一切可以在解释器中不受限制地使用。你也可以在这个文件中改变 <code class="docutils literal"><span class="pre">sys.ps1</span></code> 和 <code class="docutils literal"><span class="pre">sys.ps2</span></code> 指令。</p>
<p>如果你想要在当前目录中执行附加的启动文件，可以在全局启动文件中加入类似以下的代码：<code class="docutils literal"><span class="pre">if</span> <span class="pre">os.path.isfile('.pythonrc.py'):</span> <span class="pre">execfile('.pythonrc.py')</span></code>。如果你想要在某个脚本中使用启动文件，必须要在脚本中写入这样的语句:</p>
<div class="highlight-python"><div class="highlight"><pre><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="s">'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="k">exec</span><span class="p">(</span><span class="n">startup_file</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="tut-customize">
<span id="id7"></span><h3>15.1.4. 定制模块<a class="headerlink" href="#tut-customize" title="Permalink to this headline">¶</a></h3>
<p>Python 提供了两个钩子 (方法) 来本地化: <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>。为了见识它们，你首先需要找到你的 site-packages 的目录。启动 python 执行下面的代码:</p>
<div class="highlight-python"><div class="highlight"><pre><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/python2.7/site-packages'</span>
</pre></div>
</div>
<p>现在你可以在 site-packages 的目录下创建 <code class="file docutils literal"><span class="pre">usercustomize.py</span></code> 文件，内容就悉听尊便了。这个文件将会影响 python 的每次调用，除非启动的时候加入 <a class="reference external" href="https://docs.python.org/2.7/using/cmdline.html#cmdoption-s">-s</a> 选项禁止自动导入。</p>
<p><code class="xref py py-mod docutils literal"><span class="pre">sitecustomize</span></code> 的工作方式一样，但是是由电脑的管理账户创建以及在 <code class="xref py py-mod docutils literal"><span class="pre">usercustomize</span></code> 之前导入。具体可以参见 <a class="reference external" href="https://docs.python.org/2.7/library/site.html#module-site">site</a> 。</p>
<p class="rubric">Footnotes</p>
<table class="docutils footnote" frame="void" id="id8" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id4">[1]</a></td><td>GNU Readline包的一个问题可能禁止此功能。</td></tr>
</tbody>
</table>
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