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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="X-UA-Compatible" content="IE=Edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Curses Programming with Python — 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="Descriptor HowTo Guide" href="descriptor.html" /> <link rel="prev" title="Porting Extension Modules to Python 3" href="cporting.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="file:///usr/share/doc/python2.7/html/howto/curses.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div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;"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/howto/curses.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="descriptor.html" title="Descriptor HowTo Guide" accesskey="N">next</a> |</li> <li class="right" > <a href="cporting.html" title="Porting Extension Modules to Python 3" 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">Python HOWTOs</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="curses-programming-with-python"> <span id="curses-howto"></span><h1>Curses Programming with Python<a class="headerlink" href="#curses-programming-with-python" title="Permalink to this headline">¶</a></h1> <table class="docutils field-list" frame="void" rules="none"> <col class="field-name" /> <col class="field-body" /> <tbody valign="top"> <tr class="field-odd field"><th class="field-name">Author:</th><td class="field-body">A.M. Kuchling, Eric S. Raymond</td> </tr> <tr class="field-even field"><th class="field-name">Release:</th><td class="field-body">2.03</td> </tr> </tbody> </table> <div class="topic"> <p class="topic-title">Abstract</p> <p>This document describes how to write text-mode programs with Python 2.x, using the <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> extension module to control the display.</p> </div> <div class="section" id="what-is-curses"> <h2>What is curses?<a class="headerlink" href="#what-is-curses" title="Permalink to this headline">¶</a></h2> <p>The curses library supplies a terminal-independent screen-painting and keyboard-handling facility for text-based terminals; such terminals include VT100s, the Linux console, and the simulated terminal provided by X11 programs such as xterm and rxvt. Display terminals support various control codes to perform common operations such as moving the cursor, scrolling the screen, and erasing areas. Different terminals use widely differing codes, and often have their own minor quirks.</p> <p>In a world of X displays, one might ask “why bother”? It’s true that character-cell display terminals are an obsolete technology, but there are niches in which being able to do fancy things with them are still valuable. One is on small-footprint or embedded Unixes that don’t carry an X server. Another is for tools like OS installers and kernel configurators that may have to run before X is available.</p> <p>The curses library hides all the details of different terminals, and provides the programmer with an abstraction of a display, containing multiple non-overlapping windows. The contents of a window can be changed in various ways—adding text, erasing it, changing its appearance—and the curses library will automagically figure out what control codes need to be sent to the terminal to produce the right output.</p> <p>The curses library was originally written for BSD Unix; the later System V versions of Unix from AT&T added many enhancements and new functions. BSD curses is no longer maintained, having been replaced by ncurses, which is an open-source implementation of the AT&T interface. If you’re using an open-source Unix such as Linux or FreeBSD, your system almost certainly uses ncurses. Since most current commercial Unix versions are based on System V code, all the functions described here will probably be available. The older versions of curses carried by some proprietary Unixes may not support everything, though.</p> <p>No one has made a Windows port of the curses module. On a Windows platform, try the Console module written by Fredrik Lundh. The Console module provides cursor-addressable text output, plus full support for mouse and keyboard input, and is available from <a class="reference external" href="http://effbot.org/zone/console-index.htm">http://effbot.org/zone/console-index.htm</a>.</p> <div class="section" id="the-python-curses-module"> <h3>The Python curses module<a class="headerlink" href="#the-python-curses-module" title="Permalink to this headline">¶</a></h3> <p>Thy Python module is a fairly simple wrapper over the C functions provided by curses; if you’re already familiar with curses programming in C, it’s really easy to transfer that knowledge to Python. The biggest difference is that the Python interface makes things simpler, by merging different C functions such as <code class="xref py py-func docutils literal notranslate"><span class="pre">addstr()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">mvaddstr()</span></code>, <code class="xref py py-func docutils literal notranslate"><span class="pre">mvwaddstr()</span></code>, into a single <code class="xref py py-meth docutils literal notranslate"><span class="pre">addstr()</span></code> method. You’ll see this covered in more detail later.</p> <p>This HOWTO is simply an introduction to writing text-mode programs with curses and Python. It doesn’t attempt to be a complete guide to the curses API; for that, see the Python library guide’s section on ncurses, and the C manual pages for ncurses. It will, however, give you the basic ideas.</p> </div> </div> <div class="section" id="starting-and-ending-a-curses-application"> <h2>Starting and ending a curses application<a class="headerlink" href="#starting-and-ending-a-curses-application" title="Permalink to this headline">¶</a></h2> <p>Before doing anything, curses must be initialized. This is done by calling the <code class="xref py py-func docutils literal notranslate"><span class="pre">initscr()</span></code> function, which will determine the terminal type, send any required setup codes to the terminal, and create various internal data structures. If successful, <code class="xref py py-func docutils literal notranslate"><span class="pre">initscr()</span></code> returns a window object representing the entire screen; this is usually called <code class="docutils literal notranslate"><span class="pre">stdscr</span></code>, after the name of the corresponding C variable.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">curses</span> <span class="n">stdscr</span> <span class="o">=</span> <span class="n">curses</span><span class="o">.</span><span class="n">initscr</span><span class="p">()</span> </pre></div> </div> <p>Usually curses applications turn off automatic echoing of keys to the screen, in order to be able to read keys and only display them under certain circumstances. This requires calling the <code class="xref py py-func docutils literal notranslate"><span class="pre">noecho()</span></code> function.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">curses</span><span class="o">.</span><span class="n">noecho</span><span class="p">()</span> </pre></div> </div> <p>Applications will also commonly need to react to keys instantly, without requiring the Enter key to be pressed; this is called cbreak mode, as opposed to the usual buffered input mode.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">curses</span><span class="o">.</span><span class="n">cbreak</span><span class="p">()</span> </pre></div> </div> <p>Terminals usually return special keys, such as the cursor keys or navigation keys such as Page Up and Home, as a multibyte escape sequence. While you could write your application to expect such sequences and process them accordingly, curses can do it for you, returning a special value such as <code class="xref py py-const docutils literal notranslate"><span class="pre">curses.KEY_LEFT</span></code>. To get curses to do the job, you’ll have to enable keypad mode.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">stdscr</span><span class="o">.</span><span class="n">keypad</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> </pre></div> </div> <p>Terminating a curses application is much easier than starting one. You’ll need to call</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">curses</span><span class="o">.</span><span class="n">nocbreak</span><span class="p">();</span> <span class="n">stdscr</span><span class="o">.</span><span class="n">keypad</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span> <span class="n">curses</span><span class="o">.</span><span class="n">echo</span><span class="p">()</span> </pre></div> </div> <p>to reverse the curses-friendly terminal settings. Then call the <code class="xref py py-func docutils literal notranslate"><span class="pre">endwin()</span></code> function to restore the terminal to its original operating mode.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">curses</span><span class="o">.</span><span class="n">endwin</span><span class="p">()</span> </pre></div> </div> <p>A common problem when debugging a curses application is to get your terminal messed up when the application dies without restoring the terminal to its previous state. In Python this commonly happens when your code is buggy and raises an uncaught exception. Keys are no longer echoed to the screen when you type them, for example, which makes using the shell difficult.</p> <p>In Python you can avoid these complications and make debugging much easier by importing the <a class="reference internal" href="../library/curses.html#curses.wrapper" title="curses.wrapper"><code class="xref py py-func docutils literal notranslate"><span class="pre">curses.wrapper()</span></code></a> function. It takes a callable and does the initializations described above, also initializing colors if color support is present. It then runs your provided callable and finally deinitializes appropriately. The callable is called inside a try-catch clause which catches exceptions, performs curses deinitialization, and then passes the exception upwards. Thus, your terminal won’t be left in a funny state on exception.</p> </div> <div class="section" id="windows-and-pads"> <h2>Windows and Pads<a class="headerlink" href="#windows-and-pads" title="Permalink to this headline">¶</a></h2> <p>Windows are the basic abstraction in curses. A window object represents a rectangular area of the screen, and supports various methods to display text, erase it, allow the user to input strings, and so forth.</p> <p>The <code class="docutils literal notranslate"><span class="pre">stdscr</span></code> object returned by the <code class="xref py py-func docutils literal notranslate"><span class="pre">initscr()</span></code> function is a window object that covers the entire screen. Many programs may need only this single window, but you might wish to divide the screen into smaller windows, in order to redraw or clear them separately. The <code class="xref py py-func docutils literal notranslate"><span class="pre">newwin()</span></code> function creates a new window of a given size, returning the new window object.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">begin_x</span> <span class="o">=</span> <span class="mi">20</span><span class="p">;</span> <span class="n">begin_y</span> <span class="o">=</span> <span class="mi">7</span> <span class="n">height</span> <span class="o">=</span> <span class="mi">5</span><span class="p">;</span> <span class="n">width</span> <span class="o">=</span> <span class="mi">40</span> <span class="n">win</span> <span class="o">=</span> <span class="n">curses</span><span class="o">.</span><span class="n">newwin</span><span class="p">(</span><span class="n">height</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="n">begin_y</span><span class="p">,</span> <span class="n">begin_x</span><span class="p">)</span> </pre></div> </div> <p>A word about the coordinate system used in curses: coordinates are always passed in the order <em>y,x</em>, and the top-left corner of a window is coordinate (0,0). This breaks a common convention for handling coordinates, where the <em>x</em> coordinate usually comes first. This is an unfortunate difference from most other computer applications, but it’s been part of curses since it was first written, and it’s too late to change things now.</p> <p>When you call a method to display or erase text, the effect doesn’t immediately show up on the display. This is because curses was originally written with slow 300-baud terminal connections in mind; with these terminals, minimizing the time required to redraw the screen is very important. This lets curses accumulate changes to the screen, and display them in the most efficient manner. For example, if your program displays some characters in a window, and then clears the window, there’s no need to send the original characters because they’d never be visible.</p> <p>Accordingly, curses requires that you explicitly tell it to redraw windows, using the <code class="xref py py-func docutils literal notranslate"><span class="pre">refresh()</span></code> method of window objects. In practice, this doesn’t really complicate programming with curses much. Most programs go into a flurry of activity, and then pause waiting for a keypress or some other action on the part of the user. All you have to do is to be sure that the screen has been redrawn before pausing to wait for user input, by simply calling <code class="docutils literal notranslate"><span class="pre">stdscr.refresh()</span></code> or the <code class="xref py py-func docutils literal notranslate"><span class="pre">refresh()</span></code> method of some other relevant window.</p> <p>A pad is a special case of a window; it can be larger than the actual display screen, and only a portion of it displayed at a time. Creating a pad simply requires the pad’s height and width, while refreshing a pad requires giving the coordinates of the on-screen area where a subsection of the pad will be displayed.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">pad</span> <span class="o">=</span> <span class="n">curses</span><span class="o">.</span><span class="n">newpad</span><span class="p">(</span><span class="mi">100</span><span class="p">,</span> <span class="mi">100</span><span class="p">)</span> <span class="c1"># These loops fill the pad with letters; this is</span> <span class="c1"># explained in the next section</span> <span class="k">for</span> <span class="n">y</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">100</span><span class="p">):</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">100</span><span class="p">):</span> <span class="k">try</span><span class="p">:</span> <span class="n">pad</span><span class="o">.</span><span class="n">addch</span><span class="p">(</span><span class="n">y</span><span class="p">,</span><span class="n">x</span><span class="p">,</span> <span class="nb">ord</span><span class="p">(</span><span class="s1">'a'</span><span class="p">)</span> <span class="o">+</span> <span class="p">(</span><span class="n">x</span><span class="o">*</span><span class="n">x</span><span class="o">+</span><span class="n">y</span><span class="o">*</span><span class="n">y</span><span class="p">)</span> <span class="o">%</span> <span class="mi">26</span><span class="p">)</span> <span class="k">except</span> <span class="n">curses</span><span class="o">.</span><span class="n">error</span><span class="p">:</span> <span class="k">pass</span> <span class="c1"># Displays a section of the pad in the middle of the screen</span> <span class="n">pad</span><span class="o">.</span><span class="n">refresh</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span> <span class="mi">20</span><span class="p">,</span><span class="mi">75</span><span class="p">)</span> </pre></div> </div> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">refresh()</span></code> call displays a section of the pad in the rectangle extending from coordinate (5,5) to coordinate (20,75) on the screen; the upper left corner of the displayed section is coordinate (0,0) on the pad. Beyond that difference, pads are exactly like ordinary windows and support the same methods.</p> <p>If you have multiple windows and pads on screen there is a more efficient way to go, which will prevent annoying screen flicker at refresh time. Use the <code class="xref py py-meth docutils literal notranslate"><span class="pre">noutrefresh()</span></code> method of each window to update the data structure representing the desired state of the screen; then change the physical screen to match the desired state in one go with the function <code class="xref py py-func docutils literal notranslate"><span class="pre">doupdate()</span></code>. The normal <code class="xref py py-meth docutils literal notranslate"><span class="pre">refresh()</span></code> method calls <code class="xref py py-func docutils literal notranslate"><span class="pre">doupdate()</span></code> as its last act.</p> </div> <div class="section" id="displaying-text"> <h2>Displaying Text<a class="headerlink" href="#displaying-text" title="Permalink to this headline">¶</a></h2> <p>From a C programmer’s point of view, curses may sometimes look like a twisty maze of functions, all subtly different. For example, <code class="xref py py-func docutils literal notranslate"><span class="pre">addstr()</span></code> displays a string at the current cursor location in the <code class="docutils literal notranslate"><span class="pre">stdscr</span></code> window, while <code class="xref py py-func docutils literal notranslate"><span class="pre">mvaddstr()</span></code> moves to a given y,x coordinate first before displaying the string. <code class="xref py py-func docutils literal notranslate"><span class="pre">waddstr()</span></code> is just like <code class="xref py py-func docutils literal notranslate"><span class="pre">addstr()</span></code>, but allows specifying a window to use, instead of using <code class="docutils literal notranslate"><span class="pre">stdscr</span></code> by default. <code class="xref py py-func docutils literal notranslate"><span class="pre">mvwaddstr()</span></code> follows similarly.</p> <p>Fortunately the Python interface hides all these details; <code class="docutils literal notranslate"><span class="pre">stdscr</span></code> is a window object like any other, and methods like <code class="xref py py-func docutils literal notranslate"><span class="pre">addstr()</span></code> accept multiple argument forms. Usually there are four different forms.</p> <table border="1" class="docutils"> <colgroup> <col width="41%" /> <col width="59%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Form</th> <th class="head">Description</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><em>str</em> or <em>ch</em></td> <td>Display the string <em>str</em> or character <em>ch</em> at the current position</td> </tr> <tr class="row-odd"><td><em>str</em> or <em>ch</em>, <em>attr</em></td> <td>Display the string <em>str</em> or character <em>ch</em>, using attribute <em>attr</em> at the current position</td> </tr> <tr class="row-even"><td><em>y</em>, <em>x</em>, <em>str</em> or <em>ch</em></td> <td>Move to position <em>y,x</em> within the window, and display <em>str</em> or <em>ch</em></td> </tr> <tr class="row-odd"><td><em>y</em>, <em>x</em>, <em>str</em> or <em>ch</em>, <em>attr</em></td> <td>Move to position <em>y,x</em> within the window, and display <em>str</em> or <em>ch</em>, using attribute <em>attr</em></td> </tr> </tbody> </table> <p>Attributes allow displaying text in highlighted forms, such as in boldface, underline, reverse code, or in color. They’ll be explained in more detail in the next subsection.</p> <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">addstr()</span></code> function takes a Python string as the value to be displayed, while the <code class="xref py py-func docutils literal notranslate"><span class="pre">addch()</span></code> functions take a character, which can be either a Python string of length 1 or an integer. If it’s a string, you’re limited to displaying characters between 0 and 255. SVr4 curses provides constants for extension characters; these constants are integers greater than 255. For example, <code class="xref py py-const docutils literal notranslate"><span class="pre">ACS_PLMINUS</span></code> is a +/- symbol, and <code class="xref py py-const docutils literal notranslate"><span class="pre">ACS_ULCORNER</span></code> is the upper left corner of a box (handy for drawing borders).</p> <p>Windows remember where the cursor was left after the last operation, so if you leave out the <em>y,x</em> coordinates, the string or character will be displayed wherever the last operation left off. You can also move the cursor with the <code class="docutils literal notranslate"><span class="pre">move(y,x)</span></code> method. Because some terminals always display a flashing cursor, you may want to ensure that the cursor is positioned in some location where it won’t be distracting; it can be confusing to have the cursor blinking at some apparently random location.</p> <p>If your application doesn’t need a blinking cursor at all, you can call <code class="docutils literal notranslate"><span class="pre">curs_set(0)</span></code> to make it invisible. Equivalently, and for compatibility with older curses versions, there’s a <code class="docutils literal notranslate"><span class="pre">leaveok(bool)</span></code> function. When <em>bool</em> is true, the curses library will attempt to suppress the flashing cursor, and you won’t need to worry about leaving it in odd locations.</p> <div class="section" id="attributes-and-color"> <h3>Attributes and Color<a class="headerlink" href="#attributes-and-color" title="Permalink to this headline">¶</a></h3> <p>Characters can be displayed in different ways. Status lines in a text-based application are commonly shown in reverse video; a text viewer may need to highlight certain words. curses supports this by allowing you to specify an attribute for each cell on the screen.</p> <p>An attribute is an integer, each bit representing a different attribute. You can try to display text with multiple attribute bits set, but curses doesn’t guarantee that all the possible combinations are available, or that they’re all visually distinct. That depends on the ability of the terminal being used, so it’s safest to stick to the most commonly available attributes, listed here.</p> <table border="1" class="docutils"> <colgroup> <col width="37%" /> <col width="63%" /> </colgroup> <thead valign="bottom"> <tr class="row-odd"><th class="head">Attribute</th> <th class="head">Description</th> </tr> </thead> <tbody valign="top"> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">A_BLINK</span></code></td> <td>Blinking text</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">A_BOLD</span></code></td> <td>Extra bright or bold text</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">A_DIM</span></code></td> <td>Half bright text</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">A_REVERSE</span></code></td> <td>Reverse-video text</td> </tr> <tr class="row-even"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">A_STANDOUT</span></code></td> <td>The best highlighting mode available</td> </tr> <tr class="row-odd"><td><code class="xref py py-const docutils literal notranslate"><span class="pre">A_UNDERLINE</span></code></td> <td>Underlined text</td> </tr> </tbody> </table> <p>So, to display a reverse-video status line on the top line of the screen, you could code:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">stdscr</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="s2">"Current mode: Typing mode"</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">A_REVERSE</span><span class="p">)</span> <span class="n">stdscr</span><span class="o">.</span><span class="n">refresh</span><span class="p">()</span> </pre></div> </div> <p>The curses library also supports color on those terminals that provide it. The most common such terminal is probably the Linux console, followed by color xterms.</p> <p>To use color, you must call the <code class="xref py py-func docutils literal notranslate"><span class="pre">start_color()</span></code> function soon after calling <code class="xref py py-func docutils literal notranslate"><span class="pre">initscr()</span></code>, to initialize the default color set (the <code class="xref py py-func docutils literal notranslate"><span class="pre">curses.wrapper.wrapper()</span></code> function does this automatically). Once that’s done, the <code class="xref py py-func docutils literal notranslate"><span class="pre">has_colors()</span></code> function returns TRUE if the terminal in use can actually display color. (Note: curses uses the American spelling ‘color’, instead of the Canadian/British spelling ‘colour’. If you’re used to the British spelling, you’ll have to resign yourself to misspelling it for the sake of these functions.)</p> <p>The curses library maintains a finite number of color pairs, containing a foreground (or text) color and a background color. You can get the attribute value corresponding to a color pair with the <code class="xref py py-func docutils literal notranslate"><span class="pre">color_pair()</span></code> function; this can be bitwise-OR’ed with other attributes such as <code class="xref py py-const docutils literal notranslate"><span class="pre">A_REVERSE</span></code>, but again, such combinations are not guaranteed to work on all terminals.</p> <p>An example, which displays a line of text using color pair 1:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">stdscr</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="s2">"Pretty text"</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">color_pair</span><span class="p">(</span><span class="mi">1</span><span class="p">))</span> <span class="n">stdscr</span><span class="o">.</span><span class="n">refresh</span><span class="p">()</span> </pre></div> </div> <p>As I said before, a color pair consists of a foreground and background color. <code class="xref py py-func docutils literal notranslate"><span class="pre">start_color()</span></code> initializes 8 basic colors when it activates color mode. They are: 0:black, 1:red, 2:green, 3:yellow, 4:blue, 5:magenta, 6:cyan, and 7:white. The curses module defines named constants for each of these colors: <code class="xref py py-const docutils literal notranslate"><span class="pre">curses.COLOR_BLACK</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">curses.COLOR_RED</span></code>, and so forth.</p> <p>The <code class="docutils literal notranslate"><span class="pre">init_pair(n,</span> <span class="pre">f,</span> <span class="pre">b)</span></code> function changes the definition of color pair <em>n</em>, to foreground color f and background color b. Color pair 0 is hard-wired to white on black, and cannot be changed.</p> <p>Let’s put all this together. To change color 1 to red text on a white background, you would call:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">curses</span><span class="o">.</span><span class="n">init_pair</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_RED</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">COLOR_WHITE</span><span class="p">)</span> </pre></div> </div> <p>When you change a color pair, any text already displayed using that color pair will change to the new colors. You can also display new text in this color with:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">stdscr</span><span class="o">.</span><span class="n">addstr</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span> <span class="s2">"RED ALERT!"</span><span class="p">,</span> <span class="n">curses</span><span class="o">.</span><span class="n">color_pair</span><span class="p">(</span><span class="mi">1</span><span class="p">))</span> </pre></div> </div> <p>Very fancy terminals can change the definitions of the actual colors to a given RGB value. This lets you change color 1, which is usually red, to purple or blue or any other color you like. Unfortunately, the Linux console doesn’t support this, so I’m unable to try it out, and can’t provide any examples. You can check if your terminal can do this by calling <code class="xref py py-func docutils literal notranslate"><span class="pre">can_change_color()</span></code>, which returns TRUE if the capability is there. If you’re lucky enough to have such a talented terminal, consult your system’s man pages for more information.</p> </div> </div> <div class="section" id="user-input"> <h2>User Input<a class="headerlink" href="#user-input" title="Permalink to this headline">¶</a></h2> <p>The curses library itself offers only very simple input mechanisms. Python’s support adds a text-input widget that makes up some of the lack.</p> <p>The most common way to get input to a window is to use its <code class="xref py py-meth docutils literal notranslate"><span class="pre">getch()</span></code> method. <code class="xref py py-meth docutils literal notranslate"><span class="pre">getch()</span></code> pauses and waits for the user to hit a key, displaying it if <code class="xref py py-func docutils literal notranslate"><span class="pre">echo()</span></code> has been called earlier. You can optionally specify a coordinate to which the cursor should be moved before pausing.</p> <p>It’s possible to change this behavior with the method <code class="xref py py-meth docutils literal notranslate"><span class="pre">nodelay()</span></code>. After <code class="docutils literal notranslate"><span class="pre">nodelay(1)</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">getch()</span></code> for the window becomes non-blocking and returns <code class="docutils literal notranslate"><span class="pre">curses.ERR</span></code> (a value of -1) when no input is ready. There’s also a <code class="xref py py-func docutils literal notranslate"><span class="pre">halfdelay()</span></code> function, which can be used to (in effect) set a timer on each <code class="xref py py-meth docutils literal notranslate"><span class="pre">getch()</span></code>; if no input becomes available within a specified delay (measured in tenths of a second), curses raises an exception.</p> <p>The <code class="xref py py-meth docutils literal notranslate"><span class="pre">getch()</span></code> method returns an integer; if it’s between 0 and 255, it represents the ASCII code of the key pressed. Values greater than 255 are special keys such as Page Up, Home, or the cursor keys. You can compare the value returned to constants such as <code class="xref py py-const docutils literal notranslate"><span class="pre">curses.KEY_PPAGE</span></code>, <code class="xref py py-const docutils literal notranslate"><span class="pre">curses.KEY_HOME</span></code>, or <code class="xref py py-const docutils literal notranslate"><span class="pre">curses.KEY_LEFT</span></code>. Usually the main loop of your program will look something like this:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">while</span> <span class="mi">1</span><span class="p">:</span> <span class="n">c</span> <span class="o">=</span> <span class="n">stdscr</span><span class="o">.</span><span class="n">getch</span><span class="p">()</span> <span class="k">if</span> <span class="n">c</span> <span class="o">==</span> <span class="nb">ord</span><span class="p">(</span><span class="s1">'p'</span><span class="p">):</span> <span class="n">PrintDocument</span><span class="p">()</span> <span class="k">elif</span> <span class="n">c</span> <span class="o">==</span> <span class="nb">ord</span><span class="p">(</span><span class="s1">'q'</span><span class="p">):</span> <span class="k">break</span> <span class="c1"># Exit the while()</span> <span class="k">elif</span> <span class="n">c</span> <span class="o">==</span> <span class="n">curses</span><span class="o">.</span><span class="n">KEY_HOME</span><span class="p">:</span> <span class="n">x</span> <span class="o">=</span> <span class="n">y</span> <span class="o">=</span> <span class="mi">0</span> </pre></div> </div> <p>The <a class="reference internal" href="../library/curses.ascii.html#module-curses.ascii" title="curses.ascii: Constants and set-membership functions for ASCII characters."><code class="xref py py-mod docutils literal notranslate"><span class="pre">curses.ascii</span></code></a> module supplies ASCII class membership functions that take either integer or 1-character-string arguments; these may be useful in writing more readable tests for your command interpreters. It also supplies conversion functions that take either integer or 1-character-string arguments and return the same type. For example, <a class="reference internal" href="../library/curses.ascii.html#curses.ascii.ctrl" title="curses.ascii.ctrl"><code class="xref py py-func docutils literal notranslate"><span class="pre">curses.ascii.ctrl()</span></code></a> returns the control character corresponding to its argument.</p> <p>There’s also a method to retrieve an entire string, <code class="xref py py-const docutils literal notranslate"><span class="pre">getstr()</span></code>. It isn’t used very often, because its functionality is quite limited; the only editing keys available are the backspace key and the Enter key, which terminates the string. It can optionally be limited to a fixed number of characters.</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">curses</span><span class="o">.</span><span class="n">echo</span><span class="p">()</span> <span class="c1"># Enable echoing of characters</span> <span class="c1"># Get a 15-character string, with the cursor on the top line</span> <span class="n">s</span> <span class="o">=</span> <span class="n">stdscr</span><span class="o">.</span><span class="n">getstr</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span> <span class="mi">15</span><span class="p">)</span> </pre></div> </div> <p>The Python <a class="reference internal" href="../library/curses.html#module-curses.textpad" title="curses.textpad: Emacs-like input editing in a curses window."><code class="xref py py-mod docutils literal notranslate"><span class="pre">curses.textpad</span></code></a> module supplies something better. With it, you can turn a window into a text box that supports an Emacs-like set of keybindings. Various methods of <code class="xref py py-class docutils literal notranslate"><span class="pre">Textbox</span></code> class support editing with input validation and gathering the edit results either with or without trailing spaces. See the library documentation on <a class="reference internal" href="../library/curses.html#module-curses.textpad" title="curses.textpad: Emacs-like input editing in a curses window."><code class="xref py py-mod docutils literal notranslate"><span class="pre">curses.textpad</span></code></a> for the details.</p> </div> <div class="section" id="for-more-information"> <h2>For More Information<a class="headerlink" href="#for-more-information" title="Permalink to this headline">¶</a></h2> <p>This HOWTO didn’t cover some advanced topics, such as screen-scraping or capturing mouse events from an xterm instance. But the Python library page for the curses modules is now pretty complete. You should browse it next.</p> <p>If you’re in doubt about the detailed behavior of any of the ncurses entry points, consult the manual pages for your curses implementation, whether it’s ncurses or a proprietary Unix vendor’s. The manual pages will document any quirks, and provide complete lists of all the functions, attributes, and <code class="xref py py-const docutils literal notranslate"><span class="pre">ACS_*</span></code> characters available to you.</p> <p>Because the curses API is so large, some functions aren’t supported in the Python interface, not because they’re difficult to implement, but because no one has needed them yet. Feel free to add them and then submit a patch. Also, we don’t yet have support for the menu library associated with ncurses; feel free to add that.</p> <p>If you write an interesting little program, feel free to contribute it as another demo. We can always use more of them!</p> <p>The ncurses FAQ: <a class="reference external" href="http://invisible-island.net/ncurses/ncurses.faq.html">http://invisible-island.net/ncurses/ncurses.faq.html</a></p> </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="#">Curses Programming with Python</a><ul> <li><a class="reference internal" href="#what-is-curses">What is curses?</a><ul> <li><a class="reference internal" href="#the-python-curses-module">The Python curses module</a></li> </ul> </li> <li><a class="reference internal" href="#starting-and-ending-a-curses-application">Starting and ending a curses application</a></li> <li><a class="reference internal" href="#windows-and-pads">Windows and Pads</a></li> <li><a class="reference internal" href="#displaying-text">Displaying Text</a><ul> <li><a class="reference internal" href="#attributes-and-color">Attributes and Color</a></li> </ul> </li> <li><a class="reference internal" href="#user-input">User Input</a></li> <li><a class="reference internal" href="#for-more-information">For More Information</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="cporting.html" title="previous chapter">Porting Extension Modules to Python 3</a></p> <h4>Next topic</h4> <p class="topless"><a href="descriptor.html" title="next chapter">Descriptor HowTo Guide</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/howto/curses.rst.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3>Quick search</h3> <div class="searchformwrapper"> <form class="search" action="../search.html" method="get"> <input type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </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" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="descriptor.html" title="Descriptor HowTo Guide" >next</a> |</li> <li class="right" > <a href="cporting.html" title="Porting Extension Modules to Python 3" >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" >Python HOWTOs</a> »</li> </ul> </div> <div class="footer"> © <a href="../copyright.html">Copyright</a> 1990-2024, Python Software Foundation. <br /> The Python Software Foundation is a non-profit corporation. <a href="https://www.python.org/psf/donations/">Please donate.</a> <br /> Last updated on December 09, 2024. <a href="../bugs.html">Found a bug</a>? <br /> Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.8.5. </div> </body> </html>