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<li><a class="reference internal" href="#error-handling">16.1.1. Error Handling</a></li>
<li><a class="reference internal" href="#executable-python-scripts">16.1.2. Executable Python Scripts</a></li>
<li><a class="reference internal" href="#the-interactive-startup-file">16.1.3. The Interactive Startup File</a></li>
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<section id="appendix">
<span id="tut-appendix"></span><h1><span class="section-number">16. </span>Appendix<a class="headerlink" href="#appendix" title="Link to this heading"></a></h1>
<section id="interactive-mode">
<span id="tut-interac"></span><h2><span class="section-number">16.1. </span>Interactive Mode<a class="headerlink" href="#interactive-mode" title="Link to this heading"></a></h2>
<p>There are two variants of the interactive <a class="reference internal" href="../glossary.html#term-REPL"><span class="xref std std-term">REPL</span></a>. The classic
basic interpreter is supported on all platforms with minimal line
control capabilities.</p>
<p>On Windows, or Unix-like systems with <a class="reference internal" href="../library/curses.html#module-curses" title="curses: An interface to the curses library, providing portable terminal handling. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">curses</span></code></a> support,
a new interactive shell is used by default.
This one supports color, multiline editing, history browsing, and
paste mode. To disable color, see <a class="reference internal" href="../using/cmdline.html#using-on-controlling-color"><span class="std std-ref">Controlling color</span></a> for
details. Function keys provide some additional functionality.
<kbd class="kbd docutils literal notranslate">F1</kbd> enters the interactive help browser <a class="reference internal" href="../library/pydoc.html#module-pydoc" title="pydoc: Documentation generator and online help system."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pydoc</span></code></a>.
<kbd class="kbd docutils literal notranslate">F2</kbd> allows for browsing command-line history with neither output nor the
<a class="reference internal" href="../glossary.html#term-0"><span class="xref std std-term">&gt;&gt;&gt;</span></a> and <a class="reference internal" href="../glossary.html#term-..."><span class="xref std std-term"></span></a> prompts. <kbd class="kbd docutils literal notranslate">F3</kbd> enters “paste mode”, which
makes pasting larger blocks of code easier. Press <kbd class="kbd docutils literal notranslate">F3</kbd> to return to
the regular prompt.</p>
<p>When using the new interactive shell, exit the shell by typing <kbd class="kbd docutils literal notranslate">exit</kbd>
or <kbd class="kbd docutils literal notranslate">quit</kbd>. Adding call parentheses after those commands is not
required.</p>
<p>If the new interactive shell is not desired, it can be disabled via
the <span class="target" id="index-0"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHON_BASIC_REPL"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHON_BASIC_REPL</span></code></a> environment variable.</p>
<section id="error-handling">
<span id="tut-error"></span><h3><span class="section-number">16.1.1. </span>Error Handling<a class="headerlink" href="#error-handling" title="Link to this heading"></a></h3>
<p>When an error occurs, the interpreter prints an error message and a stack trace.
In interactive mode, it then returns to the primary prompt; when input came from
a file, it exits with a nonzero exit status after printing the stack trace.
(Exceptions handled by an <a class="reference internal" href="../reference/compound_stmts.html#except"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">except</span></code></a> clause in a <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> statement
are not errors in this context.) Some errors are unconditionally fatal and
cause an exit with a nonzero exit status; this applies to internal inconsistencies and
some cases of running out of memory. All error messages are written to the
standard error stream; normal output from executed commands is written to
standard output.</p>
<p>Typing the interrupt character (usually <kbd class="kbd docutils literal notranslate">Control</kbd>-<kbd class="kbd docutils literal notranslate">C</kbd> or <kbd class="kbd docutils literal notranslate">Delete</kbd>) to the primary or
secondary prompt cancels the input and returns to the primary prompt. <a class="footnote-reference brackets" href="#id2" id="id1" role="doc-noteref"><span class="fn-bracket">[</span>1<span class="fn-bracket">]</span></a>
Typing an interrupt while a command is executing raises the
<a class="reference internal" href="../library/exceptions.html#KeyboardInterrupt" title="KeyboardInterrupt"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyboardInterrupt</span></code></a> exception, which may be handled by a <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a>
statement.</p>
</section>
<section id="executable-python-scripts">
<span id="tut-scripts"></span><h3><span class="section-number">16.1.2. </span>Executable Python Scripts<a class="headerlink" href="#executable-python-scripts" title="Link to this heading"></a></h3>
<p>On BSDish Unix systems, Python scripts can be made directly executable, like
shell scripts, by putting the line</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="ch">#!/usr/bin/env python3</span>
</pre></div>
</div>
<p>(assuming that the interpreter is on the users <span class="target" id="index-1"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PATH</span></code>) at the beginning
of the script and giving the file an executable mode. The <code class="docutils literal notranslate"><span class="pre">#!</span></code> must be the
first two characters of the file. On some platforms, this first line must end
with a Unix-style line ending (<code class="docutils literal notranslate"><span class="pre">'\n'</span></code>), not a Windows (<code class="docutils literal notranslate"><span class="pre">'\r\n'</span></code>) line
ending. Note that the hash, or pound, character, <code class="docutils literal notranslate"><span class="pre">'#'</span></code>, is used to start a
comment in Python.</p>
<p>The script can be given an executable mode, or permission, using the
<strong class="program">chmod</strong> command.</p>
<div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>chmod<span class="w"> </span>+x<span class="w"> </span>myscript.py
</pre></div>
</div>
<p>On Windows systems, there is no notion of an “executable mode”. The Python
installer automatically associates <code class="docutils literal notranslate"><span class="pre">.py</span></code> files with <code class="docutils literal notranslate"><span class="pre">python.exe</span></code> so that
a double-click on a Python file will run it as a script. The extension can
also be <code class="docutils literal notranslate"><span class="pre">.pyw</span></code>, in that case, the console window that normally appears is
suppressed.</p>
</section>
<section id="the-interactive-startup-file">
<span id="tut-startup"></span><h3><span class="section-number">16.1.3. </span>The Interactive Startup File<a class="headerlink" href="#the-interactive-startup-file" title="Link to this heading"></a></h3>
<p>When you use Python interactively, it is frequently handy to have some standard
commands executed every time the interpreter is started. You can do this by
setting an environment variable named <span class="target" id="index-2"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONSTARTUP"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONSTARTUP</span></code></a> to the name of a
file containing your start-up commands. This is similar to the <code class="file docutils literal notranslate"><span class="pre">.profile</span></code>
feature of the Unix shells.</p>
<p>This file is only read in interactive sessions, not when Python reads commands
from a script, and not when <code class="file docutils literal notranslate"><span class="pre">/dev/tty</span></code> is given as the explicit source of
commands (which otherwise behaves like an interactive session). It is executed
in the same namespace where interactive commands are executed, so that objects
that it defines or imports can be used without qualification in the interactive
session. You can also change the prompts <code class="docutils literal notranslate"><span class="pre">sys.ps1</span></code> and <code class="docutils literal notranslate"><span class="pre">sys.ps2</span></code> in this
file.</p>
<p>If you want to read an additional start-up file from the current directory, you
can program this in the global start-up file using code like <code class="docutils literal notranslate"><span class="pre">if</span>
<span class="pre">os.path.isfile('.pythonrc.py'):</span> <span class="pre">exec(open('.pythonrc.py').read())</span></code>.
If you want to use the startup file in a script, you must do this explicitly
in the script:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span><span class="w"> </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">&#39;PYTHONSTARTUP&#39;</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>
</section>
<section id="the-customization-modules">
<span id="tut-customize"></span><h3><span class="section-number">16.1.4. </span>The Customization Modules<a class="headerlink" href="#the-customization-modules" title="Link to this heading"></a></h3>
<p>Python provides two hooks to let you customize it: <span class="target" id="index-3"></span>sitecustomize and
<span class="target" id="index-4"></span>usercustomize. To see how it works, you need first to find the location
of your user site-packages directory. Start Python and run this code:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span><span class="w"> </span><span class="nn">site</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">site</span><span class="o">.</span><span class="n">getusersitepackages</span><span class="p">()</span>
<span class="go">&#39;/home/user/.local/lib/python3.x/site-packages&#39;</span>
</pre></div>
</div>
<p>Now you can create a file named <code class="file docutils literal notranslate"><span class="pre">usercustomize.py</span></code> in that directory and
put anything you want in it. It will affect every invocation of Python, unless
it is started with the <a class="reference internal" href="../using/cmdline.html#cmdoption-s"><code class="xref std std-option docutils literal notranslate"><span class="pre">-s</span></code></a> option to disable the automatic import.</p>
<p><span class="target" id="index-5"></span>sitecustomize works in the same way, but is typically created by an
administrator of the computer in the global site-packages directory, and is
imported before <span class="target" id="index-6"></span>usercustomize. See the documentation of the <a class="reference internal" href="../library/site.html#module-site" title="site: Module responsible for site-specific configuration."><code class="xref py py-mod docutils literal notranslate"><span class="pre">site</span></code></a>
module for more details.</p>
<p class="rubric">Footnotes</p>
<aside class="footnote-list brackets">
<aside class="footnote brackets" id="id2" role="doc-footnote">
<span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id1">1</a><span class="fn-bracket">]</span></span>
<p>A problem with the GNU Readline package may prevent this.</p>
</aside>
</aside>
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<li><a class="reference internal" href="#">16. Appendix</a><ul>
<li><a class="reference internal" href="#interactive-mode">16.1. Interactive Mode</a><ul>
<li><a class="reference internal" href="#error-handling">16.1.1. Error Handling</a></li>
<li><a class="reference internal" href="#executable-python-scripts">16.1.2. Executable Python Scripts</a></li>
<li><a class="reference internal" href="#the-interactive-startup-file">16.1.3. The Interactive Startup File</a></li>
<li><a class="reference internal" href="#the-customization-modules">16.1.4. The Customization Modules</a></li>
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