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Interactive Input Editing and History Substitution — Python 2.7.18 documentation</title> <link rel="stylesheet" href="../_static/classic.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 2.7.18 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="14. Floating Point Arithmetic: Issues and Limitations" href="floatingpoint.html" /> <link rel="prev" title="12. What Now?" href="whatnow.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/tutorial/interactive.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> </head><body> <div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"> This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>. You should install the python3 and python3-doc packages and read the <a href="file:///usr/share/doc/python3-doc/html/tutorial/interactive.html"> Python documentation for the Python3 version packaged in this release</a>. </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="floatingpoint.html" title="14. Floating Point Arithmetic: Issues and Limitations" accesskey="N">next</a> |</li> <li class="right" > <a href="whatnow.html" title="12. What Now?" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.18 documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" accesskey="U">The Python Tutorial</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="interactive-input-editing-and-history-substitution"> <span id="tut-interacting"></span><h1>13. Interactive Input Editing and History Substitution<a class="headerlink" href="#interactive-input-editing-and-history-substitution" title="Permalink to this headline">¶</a></h1> <p>Some versions of the Python interpreter support editing of the current input line and history substitution, similar to facilities found in the Korn shell and the GNU Bash shell. This is implemented using the <a class="reference external" href="https://tiswww.case.edu/php/chet/readline/rltop.html">GNU Readline</a> library, which supports Emacs-style and vi-style editing. This library has its own documentation which I won’t duplicate here; however, the basics are easily explained. The interactive editing and history described here are optionally available in the Unix and Cygwin versions of the interpreter.</p> <p>This chapter does <em>not</em> document the editing facilities of Mark Hammond’s PythonWin package or the Tk-based environment, IDLE, distributed with Python. The command line history recall which operates within DOS boxes on NT and some other DOS and Windows flavors is yet another beast.</p> <div class="section" id="line-editing"> <span id="tut-lineediting"></span><h2>13.1. Line Editing<a class="headerlink" href="#line-editing" title="Permalink to this headline">¶</a></h2> <p>If supported, input line editing is active whenever the interpreter prints a primary or secondary prompt. The current line can be edited using the conventional Emacs control characters. The most important of these are: <kbd class="kbd docutils literal notranslate">C-A</kbd> (Control-A) moves the cursor to the beginning of the line, <kbd class="kbd docutils literal notranslate">C-E</kbd> to the end, <kbd class="kbd docutils literal notranslate">C-B</kbd> moves it one position to the left, <kbd class="kbd docutils literal notranslate">C-F</kbd> to the right. Backspace erases the character to the left of the cursor, <kbd class="kbd docutils literal notranslate">C-D</kbd> the character to its right. <kbd class="kbd docutils literal notranslate">C-K</kbd> kills (erases) the rest of the line to the right of the cursor, <kbd class="kbd docutils literal notranslate">C-Y</kbd> yanks back the last killed string. <kbd class="kbd docutils literal notranslate">C-underscore</kbd> undoes the last change you made; it can be repeated for cumulative effect.</p> </div> <div class="section" id="history-substitution"> <span id="tut-history"></span><h2>13.2. History Substitution<a class="headerlink" href="#history-substitution" title="Permalink to this headline">¶</a></h2> <p>History substitution works as follows. All non-empty input lines issued are saved in a history buffer, and when a new prompt is given you are positioned on a new line at the bottom of this buffer. <kbd class="kbd docutils literal notranslate">C-P</kbd> moves one line up (back) in the history buffer, <kbd class="kbd docutils literal notranslate">C-N</kbd> moves one down. Any line in the history buffer can be edited; an asterisk appears in front of the prompt to mark a line as modified. Pressing the <kbd class="kbd docutils literal notranslate">Return</kbd> key passes the current line to the interpreter. <kbd class="kbd docutils literal notranslate">C-R</kbd> starts an incremental reverse search; <kbd class="kbd docutils literal notranslate">C-S</kbd> starts a forward search.</p> </div> <div class="section" id="key-bindings"> <span id="tut-keybindings"></span><h2>13.3. Key Bindings<a class="headerlink" href="#key-bindings" title="Permalink to this headline">¶</a></h2> <p>The key bindings and some other parameters of the Readline library can be customized by placing commands in an initialization file called <code class="file docutils literal notranslate"><span class="pre">~/.inputrc</span></code>. Key bindings have the form</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">key</span><span class="o">-</span><span class="n">name</span><span class="p">:</span> <span class="n">function</span><span class="o">-</span><span class="n">name</span> </pre></div> </div> <p>or</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="s2">"string"</span><span class="p">:</span> <span class="n">function</span><span class="o">-</span><span class="n">name</span> </pre></div> </div> <p>and options can be set with</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nb">set</span> <span class="n">option</span><span class="o">-</span><span class="n">name</span> <span class="n">value</span> </pre></div> </div> <p>For example:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="c1"># I prefer vi-style editing:</span> <span class="nb">set</span> <span class="n">editing</span><span class="o">-</span><span class="n">mode</span> <span class="n">vi</span> <span class="c1"># Edit using a single line:</span> <span class="nb">set</span> <span class="n">horizontal</span><span class="o">-</span><span class="n">scroll</span><span class="o">-</span><span class="n">mode</span> <span class="n">On</span> <span class="c1"># Rebind some keys:</span> <span class="n">Meta</span><span class="o">-</span><span class="n">h</span><span class="p">:</span> <span class="n">backward</span><span class="o">-</span><span class="n">kill</span><span class="o">-</span><span class="n">word</span> <span class="s2">"\C-u"</span><span class="p">:</span> <span class="n">universal</span><span class="o">-</span><span class="n">argument</span> <span class="s2">"\C-x\C-r"</span><span class="p">:</span> <span class="n">re</span><span class="o">-</span><span class="n">read</span><span class="o">-</span><span class="n">init</span><span class="o">-</span><span class="n">file</span> </pre></div> </div> <p>Note that the default binding for <kbd class="kbd docutils literal notranslate">Tab</kbd> in Python is to insert a <kbd class="kbd docutils literal notranslate">Tab</kbd> character instead of Readline’s default filename completion function. If you insist, you can override this by putting</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">Tab</span><span class="p">:</span> <span class="n">complete</span> </pre></div> </div> <p>in your <code class="file docutils literal notranslate"><span class="pre">~/.inputrc</span></code>. (Of course, this makes it harder to type indented continuation lines if you’re accustomed to using <kbd class="kbd docutils literal notranslate">Tab</kbd> for that purpose.)</p> <p id="index-0">Automatic completion of variable and module names is optionally available. To enable it in the interpreter’s interactive mode, add the following to your startup file: <a class="footnote-reference" href="#id2" id="id1">[1]</a></p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">rlcompleter</span><span class="o">,</span> <span class="nn">readline</span> <span class="n">readline</span><span class="o">.</span><span class="n">parse_and_bind</span><span class="p">(</span><span class="s1">'tab: complete'</span><span class="p">)</span> </pre></div> </div> <p>This binds the <kbd class="kbd docutils literal notranslate">Tab</kbd> key to the completion function, so hitting the <kbd class="kbd docutils literal notranslate">Tab</kbd> key twice suggests completions; it looks at Python statement names, the current local variables, and the available module names. For dotted expressions such as <code class="docutils literal notranslate"><span class="pre">string.a</span></code>, it will evaluate the expression up to the final <code class="docutils literal notranslate"><span class="pre">'.'</span></code> and then suggest completions from the attributes of the resulting object. Note that this may execute application-defined code if an object with a <a class="reference internal" href="../reference/datamodel.html#object.__getattr__" title="object.__getattr__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getattr__()</span></code></a> method is part of the expression.</p> <p>A more capable startup file might look like this example. Note that this deletes the names it creates once they are no longer needed; this is done since the startup file is executed in the same namespace as the interactive commands, and removing the names avoids creating side effects in the interactive environment. You may find it convenient to keep some of the imported modules, such as <a class="reference internal" href="../library/os.html#module-os" title="os: Miscellaneous operating system interfaces."><code class="xref py py-mod docutils literal notranslate"><span class="pre">os</span></code></a>, which turn out to be needed in most sessions with the interpreter.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="c1"># Add auto-completion and a stored history file of commands to your Python</span> <span class="c1"># interactive interpreter. Requires Python 2.0+, readline. Autocomplete is</span> <span class="c1"># bound to the Esc key by default (you can change it - see readline docs).</span> <span class="c1">#</span> <span class="c1"># Store the file in ~/.pystartup, and set an environment variable to point</span> <span class="c1"># to it: "export PYTHONSTARTUP=~/.pystartup" in bash.</span> <span class="kn">import</span> <span class="nn">atexit</span> <span class="kn">import</span> <span class="nn">os</span> <span class="kn">import</span> <span class="nn">readline</span> <span class="kn">import</span> <span class="nn">rlcompleter</span> <span class="n">historyPath</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">expanduser</span><span class="p">(</span><span class="s2">"~/.pyhistory"</span><span class="p">)</span> <span class="k">def</span> <span class="nf">save_history</span><span class="p">(</span><span class="n">historyPath</span><span class="o">=</span><span class="n">historyPath</span><span class="p">):</span> <span class="kn">import</span> <span class="nn">readline</span> <span class="n">readline</span><span class="o">.</span><span class="n">write_history_file</span><span class="p">(</span><span class="n">historyPath</span><span class="p">)</span> <span class="k">if</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">exists</span><span class="p">(</span><span class="n">historyPath</span><span class="p">):</span> <span class="n">readline</span><span class="o">.</span><span class="n">read_history_file</span><span class="p">(</span><span class="n">historyPath</span><span class="p">)</span> <span class="n">atexit</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">save_history</span><span class="p">)</span> <span class="k">del</span> <span class="n">os</span><span class="p">,</span> <span class="n">atexit</span><span class="p">,</span> <span class="n">readline</span><span class="p">,</span> <span class="n">rlcompleter</span><span class="p">,</span> <span class="n">save_history</span><span class="p">,</span> <span class="n">historyPath</span> </pre></div> </div> </div> <div class="section" id="alternatives-to-the-interactive-interpreter"> <span id="tut-commentary"></span><h2>13.4. Alternatives to the Interactive Interpreter<a class="headerlink" href="#alternatives-to-the-interactive-interpreter" title="Permalink to this headline">¶</a></h2> <p>This facility is an enormous step forward compared to earlier versions of the interpreter; however, some wishes are left: It would be nice if the proper indentation were suggested on continuation lines (the parser knows if an indent token is required next). The completion mechanism might use the interpreter’s symbol table. A command to check (or even suggest) matching parentheses, quotes, etc., would also be useful.</p> <p>One alternative enhanced interactive interpreter that has been around for quite some time is <a class="reference external" href="http://ipython.scipy.org/">IPython</a>, which features tab completion, object exploration and advanced history management. It can also be thoroughly customized and embedded into other applications. Another similar enhanced interactive environment is <a class="reference external" href="http://www.bpython-interpreter.org/">bpython</a>.</p> <p class="rubric">Footnotes</p> <table class="docutils footnote" frame="void" id="id2" rules="none"> <colgroup><col class="label" /><col /></colgroup> <tbody valign="top"> <tr><td class="label"><a class="fn-backref" href="#id1">[1]</a></td><td>Python will execute the contents of a file identified by the <span class="target" id="index-1"></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> environment variable when you start an interactive interpreter. To customize Python even for non-interactive mode, see <a class="reference internal" href="appendix.html#tut-customize"><span class="std std-ref">The Customization Modules</span></a>.</td></tr> </tbody> </table> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#">13. Interactive Input Editing and History Substitution</a><ul> <li><a class="reference internal" href="#line-editing">13.1. Line Editing</a></li> <li><a class="reference internal" href="#history-substitution">13.2. History Substitution</a></li> <li><a class="reference internal" href="#key-bindings">13.3. Key Bindings</a></li> <li><a class="reference internal" href="#alternatives-to-the-interactive-interpreter">13.4. Alternatives to the Interactive Interpreter</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="whatnow.html" title="previous chapter">12. What Now?</a></p> <h4>Next topic</h4> <p class="topless"><a href="floatingpoint.html" title="next chapter">14. 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