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  193.   <section id="module-cmd">

  194. <span id="cmd-support-for-line-oriented-command-interpreters"></span><h1><a class="reference internal" href="#module-cmd" title="cmd: Build line-oriented command interpreters."><code class="xref py py-mod docutils literal notranslate"><span class="pre">cmd</span></code></a> — Support for line-oriented command interpreters<a class="headerlink" href="#module-cmd" title="Link to this heading">¶</a></h1>

  195. <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.12/Lib/cmd.py">Lib/cmd.py</a></p>

  196. <hr class="docutils" />

  197. <p>The <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a> class provides a simple framework for writing line-oriented

  198. command interpreters.  These are often useful for test harnesses, administrative

  199. tools, and prototypes that will later be wrapped in a more sophisticated

  200. interface.</p>

  201. <dl class="py class">

  202. <dt class="sig sig-object py" id="cmd.Cmd">

  203. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">cmd.</span></span><span class="sig-name descname"><span class="pre">Cmd</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">completekey</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">'tab'</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">stdin</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">stdout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd" title="Link to this definition">¶</a></dt>

  204. <dd><p>A <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a> instance or subclass instance is a line-oriented interpreter

  205. framework.  There is no good reason to instantiate <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a> itself; rather,

  206. it’s useful as a superclass of an interpreter class you define yourself in order

  207. to inherit <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a>’s methods and encapsulate action methods.</p>

  208. <p>The optional argument <em>completekey</em> is the <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">readline</span></code></a> name of a completion

  209. key; it defaults to <kbd class="kbd docutils literal notranslate">Tab</kbd>. If <em>completekey</em> is not <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> and

  210. <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">readline</span></code></a> is available, command completion is done automatically.</p>

  211. <p>The optional arguments <em>stdin</em> and <em>stdout</em> specify the  input and output file

  212. objects that the Cmd instance or subclass  instance will use for input and

  213. output. If not specified, they will default to <a class="reference internal" href="sys.html#sys.stdin" title="sys.stdin"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stdin</span></code></a> and

  214. <a class="reference internal" href="sys.html#sys.stdout" title="sys.stdout"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stdout</span></code></a>.</p>

  215. <p>If you want a given <em>stdin</em> to be used, make sure to set the instance’s

  216. <a class="reference internal" href="#cmd.Cmd.use_rawinput" title="cmd.Cmd.use_rawinput"><code class="xref py py-attr docutils literal notranslate"><span class="pre">use_rawinput</span></code></a> attribute to <code class="docutils literal notranslate"><span class="pre">False</span></code>, otherwise <em>stdin</em> will be

  217. ignored.</p>

  218. </dd></dl>

  219. 

  220. <section id="cmd-objects">

  221. <span id="id1"></span><h2>Cmd Objects<a class="headerlink" href="#cmd-objects" title="Link to this heading">¶</a></h2>

  222. <p>A <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a> instance has the following methods:</p>

  223. <dl class="py method">

  224. <dt class="sig sig-object py" id="cmd.Cmd.cmdloop">

  225. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">cmdloop</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">intro</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.cmdloop" title="Link to this definition">¶</a></dt>

  226. <dd><p>Repeatedly issue a prompt, accept input, parse an initial prefix off the

  227. received input, and dispatch to action methods, passing them the remainder of

  228. the line as argument.</p>

  229. <p>The optional argument is a banner or intro string to be issued before the first

  230. prompt (this overrides the <a class="reference internal" href="#cmd.Cmd.intro" title="cmd.Cmd.intro"><code class="xref py py-attr docutils literal notranslate"><span class="pre">intro</span></code></a> class attribute).</p>

  231. <p>If the <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">readline</span></code></a> module is loaded, input will automatically inherit

  232. <strong class="program">bash</strong>-like history-list editing (e.g. <kbd class="kbd compound docutils literal notranslate"><kbd class="kbd docutils literal notranslate">Control</kbd>-<kbd class="kbd docutils literal notranslate">P</kbd></kbd> scrolls back

  233. to the last command, <kbd class="kbd compound docutils literal notranslate"><kbd class="kbd docutils literal notranslate">Control</kbd>-<kbd class="kbd docutils literal notranslate">N</kbd></kbd> forward to the next one, <kbd class="kbd compound docutils literal notranslate"><kbd class="kbd docutils literal notranslate">Control</kbd>-<kbd class="kbd docutils literal notranslate">F</kbd></kbd>

  234. moves the cursor to the right non-destructively, <kbd class="kbd compound docutils literal notranslate"><kbd class="kbd docutils literal notranslate">Control</kbd>-<kbd class="kbd docutils literal notranslate">B</kbd></kbd> moves the

  235. cursor to the left non-destructively, etc.).</p>

  236. <p>An end-of-file on input is passed back as the string <code class="docutils literal notranslate"><span class="pre">'EOF'</span></code>.</p>

  237. <p id="index-0">An interpreter instance will recognize a command name <code class="docutils literal notranslate"><span class="pre">foo</span></code> if and only if it

  238. has a method <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_foo()</span></code>.  As a special case, a line beginning with the

  239. character <code class="docutils literal notranslate"><span class="pre">'?'</span></code> is dispatched to the method <a class="reference internal" href="#cmd.Cmd.do_help" title="cmd.Cmd.do_help"><code class="xref py py-meth docutils literal notranslate"><span class="pre">do_help()</span></code></a>.  As another

  240. special case, a line beginning with the character <code class="docutils literal notranslate"><span class="pre">'!'</span></code> is dispatched to the

  241. method <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_shell()</span></code> (if such a method is defined).</p>

  242. <p>This method will return when the <a class="reference internal" href="#cmd.Cmd.postcmd" title="cmd.Cmd.postcmd"><code class="xref py py-meth docutils literal notranslate"><span class="pre">postcmd()</span></code></a> method returns a true value.

  243. The <em>stop</em> argument to <a class="reference internal" href="#cmd.Cmd.postcmd" title="cmd.Cmd.postcmd"><code class="xref py py-meth docutils literal notranslate"><span class="pre">postcmd()</span></code></a> is the return value from the command’s

  244. corresponding <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_*()</span></code> method.</p>

  245. <p>If completion is enabled, completing commands will be done automatically, and

  246. completing of commands args is done by calling <code class="xref py py-meth docutils literal notranslate"><span class="pre">complete_foo()</span></code> with

  247. arguments <em>text</em>, <em>line</em>, <em>begidx</em>, and <em>endidx</em>.  <em>text</em> is the string prefix

  248. we are attempting to match: all returned matches must begin with it. <em>line</em> is

  249. the current input line with leading whitespace removed, <em>begidx</em> and <em>endidx</em>

  250. are the beginning and ending indexes of the prefix text, which could be used to

  251. provide different completion depending upon which position the argument is in.</p>

  252. </dd></dl>

  253. 

  254. <dl class="py method">

  255. <dt class="sig sig-object py" id="cmd.Cmd.do_help">

  256. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">do_help</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">arg</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.do_help" title="Link to this definition">¶</a></dt>

  257. <dd><p>All subclasses of <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a> inherit a predefined <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_help()</span></code>.  This

  258. method, called with an argument <code class="docutils literal notranslate"><span class="pre">'bar'</span></code>, invokes the corresponding method

  259. <code class="xref py py-meth docutils literal notranslate"><span class="pre">help_bar()</span></code>, and if that is not present, prints the docstring of

  260. <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_bar()</span></code>, if available.  With no argument, <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_help()</span></code> lists all

  261. available help topics (that is, all commands with corresponding

  262. <code class="xref py py-meth docutils literal notranslate"><span class="pre">help_*()</span></code> methods or commands that have docstrings), and also lists any

  263. undocumented commands.</p>

  264. </dd></dl>

  265. 

  266. <dl class="py method">

  267. <dt class="sig sig-object py" id="cmd.Cmd.onecmd">

  268. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">onecmd</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">str</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.onecmd" title="Link to this definition">¶</a></dt>

  269. <dd><p>Interpret the argument as though it had been typed in response to the prompt.

  270. This may be overridden, but should not normally need to be; see the

  271. <a class="reference internal" href="#cmd.Cmd.precmd" title="cmd.Cmd.precmd"><code class="xref py py-meth docutils literal notranslate"><span class="pre">precmd()</span></code></a> and <a class="reference internal" href="#cmd.Cmd.postcmd" title="cmd.Cmd.postcmd"><code class="xref py py-meth docutils literal notranslate"><span class="pre">postcmd()</span></code></a> methods for useful execution hooks.  The

  272. return value is a flag indicating whether interpretation of commands by the

  273. interpreter should stop.  If there is a <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_*()</span></code> method for the command

  274. <em>str</em>, the return value of that method is returned, otherwise the return value

  275. from the <a class="reference internal" href="#cmd.Cmd.default" title="cmd.Cmd.default"><code class="xref py py-meth docutils literal notranslate"><span class="pre">default()</span></code></a> method is returned.</p>

  276. </dd></dl>

  277. 

  278. <dl class="py method">

  279. <dt class="sig sig-object py" id="cmd.Cmd.emptyline">

  280. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">emptyline</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.emptyline" title="Link to this definition">¶</a></dt>

  281. <dd><p>Method called when an empty line is entered in response to the prompt. If this

  282. method is not overridden, it repeats the last nonempty command entered.</p>

  283. </dd></dl>

  284. 

  285. <dl class="py method">

  286. <dt class="sig sig-object py" id="cmd.Cmd.default">

  287. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">default</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">line</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.default" title="Link to this definition">¶</a></dt>

  288. <dd><p>Method called on an input line when the command prefix is not recognized. If

  289. this method is not overridden, it prints an error message and returns.</p>

  290. </dd></dl>

  291. 

  292. <dl class="py method">

  293. <dt class="sig sig-object py" id="cmd.Cmd.completedefault">

  294. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">completedefault</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">text</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">line</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">begidx</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">endidx</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.completedefault" title="Link to this definition">¶</a></dt>

  295. <dd><p>Method called to complete an input line when no command-specific

  296. <code class="xref py py-meth docutils literal notranslate"><span class="pre">complete_*()</span></code> method is available.  By default, it returns an empty list.</p>

  297. </dd></dl>

  298. 

  299. <dl class="py method">

  300. <dt class="sig sig-object py" id="cmd.Cmd.columnize">

  301. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">columnize</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">list</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">displaywidth</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">80</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.columnize" title="Link to this definition">¶</a></dt>

  302. <dd><p>Method called to display a list of strings as a compact set of columns.

  303. Each column is only as wide as necessary.

  304. Columns are separated by two spaces for readability.</p>

  305. </dd></dl>

  306. 

  307. <dl class="py method">

  308. <dt class="sig sig-object py" id="cmd.Cmd.precmd">

  309. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">precmd</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">line</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.precmd" title="Link to this definition">¶</a></dt>

  310. <dd><p>Hook method executed just before the command line <em>line</em> is interpreted, but

  311. after the input prompt is generated and issued.  This method is a stub in

  312. <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a>; it exists to be overridden by subclasses.  The return value is

  313. used as the command which will be executed by the <a class="reference internal" href="#cmd.Cmd.onecmd" title="cmd.Cmd.onecmd"><code class="xref py py-meth docutils literal notranslate"><span class="pre">onecmd()</span></code></a> method; the

  314. <a class="reference internal" href="#cmd.Cmd.precmd" title="cmd.Cmd.precmd"><code class="xref py py-meth docutils literal notranslate"><span class="pre">precmd()</span></code></a> implementation may re-write the command or simply return <em>line</em>

  315. unchanged.</p>

  316. </dd></dl>

  317. 

  318. <dl class="py method">

  319. <dt class="sig sig-object py" id="cmd.Cmd.postcmd">

  320. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">postcmd</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">stop</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">line</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.postcmd" title="Link to this definition">¶</a></dt>

  321. <dd><p>Hook method executed just after a command dispatch is finished.  This method is

  322. a stub in <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a>; it exists to be overridden by subclasses.  <em>line</em> is the

  323. command line which was executed, and <em>stop</em> is a flag which indicates whether

  324. execution will be terminated after the call to <a class="reference internal" href="#cmd.Cmd.postcmd" title="cmd.Cmd.postcmd"><code class="xref py py-meth docutils literal notranslate"><span class="pre">postcmd()</span></code></a>; this will be the

  325. return value of the <a class="reference internal" href="#cmd.Cmd.onecmd" title="cmd.Cmd.onecmd"><code class="xref py py-meth docutils literal notranslate"><span class="pre">onecmd()</span></code></a> method.  The return value of this method will

  326. be used as the new value for the internal flag which corresponds to <em>stop</em>;

  327. returning false will cause interpretation to continue.</p>

  328. </dd></dl>

  329. 

  330. <dl class="py method">

  331. <dt class="sig sig-object py" id="cmd.Cmd.preloop">

  332. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">preloop</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.preloop" title="Link to this definition">¶</a></dt>

  333. <dd><p>Hook method executed once when <a class="reference internal" href="#cmd.Cmd.cmdloop" title="cmd.Cmd.cmdloop"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cmdloop()</span></code></a> is called.  This method is a stub

  334. in <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a>; it exists to be overridden by subclasses.</p>

  335. </dd></dl>

  336. 

  337. <dl class="py method">

  338. <dt class="sig sig-object py" id="cmd.Cmd.postloop">

  339. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">postloop</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#cmd.Cmd.postloop" title="Link to this definition">¶</a></dt>

  340. <dd><p>Hook method executed once when <a class="reference internal" href="#cmd.Cmd.cmdloop" title="cmd.Cmd.cmdloop"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cmdloop()</span></code></a> is about to return. This method

  341. is a stub in <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a>; it exists to be overridden by subclasses.</p>

  342. </dd></dl>

  343. 

  344. <p>Instances of <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a> subclasses have some public instance variables:</p>

  345. <dl class="py attribute">

  346. <dt class="sig sig-object py" id="cmd.Cmd.prompt">

  347. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">prompt</span></span><a class="headerlink" href="#cmd.Cmd.prompt" title="Link to this definition">¶</a></dt>

  348. <dd><p>The prompt issued to solicit input.</p>

  349. </dd></dl>

  350. 

  351. <dl class="py attribute">

  352. <dt class="sig sig-object py" id="cmd.Cmd.identchars">

  353. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">identchars</span></span><a class="headerlink" href="#cmd.Cmd.identchars" title="Link to this definition">¶</a></dt>

  354. <dd><p>The string of characters accepted for the command prefix.</p>

  355. </dd></dl>

  356. 

  357. <dl class="py attribute">

  358. <dt class="sig sig-object py" id="cmd.Cmd.lastcmd">

  359. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">lastcmd</span></span><a class="headerlink" href="#cmd.Cmd.lastcmd" title="Link to this definition">¶</a></dt>

  360. <dd><p>The last nonempty command prefix seen.</p>

  361. </dd></dl>

  362. 

  363. <dl class="py attribute">

  364. <dt class="sig sig-object py" id="cmd.Cmd.cmdqueue">

  365. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">cmdqueue</span></span><a class="headerlink" href="#cmd.Cmd.cmdqueue" title="Link to this definition">¶</a></dt>

  366. <dd><p>A list of queued input lines.  The cmdqueue list is checked in

  367. <a class="reference internal" href="#cmd.Cmd.cmdloop" title="cmd.Cmd.cmdloop"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cmdloop()</span></code></a> when new input is needed; if it is nonempty, its elements

  368. will be processed in order, as if entered at the prompt.</p>

  369. </dd></dl>

  370. 

  371. <dl class="py attribute">

  372. <dt class="sig sig-object py" id="cmd.Cmd.intro">

  373. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">intro</span></span><a class="headerlink" href="#cmd.Cmd.intro" title="Link to this definition">¶</a></dt>

  374. <dd><p>A string to issue as an intro or banner.  May be overridden by giving the

  375. <a class="reference internal" href="#cmd.Cmd.cmdloop" title="cmd.Cmd.cmdloop"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cmdloop()</span></code></a> method an argument.</p>

  376. </dd></dl>

  377. 

  378. <dl class="py attribute">

  379. <dt class="sig sig-object py" id="cmd.Cmd.doc_header">

  380. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">doc_header</span></span><a class="headerlink" href="#cmd.Cmd.doc_header" title="Link to this definition">¶</a></dt>

  381. <dd><p>The header to issue if the help output has a section for documented commands.</p>

  382. </dd></dl>

  383. 

  384. <dl class="py attribute">

  385. <dt class="sig sig-object py" id="cmd.Cmd.misc_header">

  386. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">misc_header</span></span><a class="headerlink" href="#cmd.Cmd.misc_header" title="Link to this definition">¶</a></dt>

  387. <dd><p>The header to issue if the help output has a section for miscellaneous  help

  388. topics (that is, there are <code class="xref py py-meth docutils literal notranslate"><span class="pre">help_*()</span></code> methods without corresponding

  389. <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_*()</span></code> methods).</p>

  390. </dd></dl>

  391. 

  392. <dl class="py attribute">

  393. <dt class="sig sig-object py" id="cmd.Cmd.undoc_header">

  394. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">undoc_header</span></span><a class="headerlink" href="#cmd.Cmd.undoc_header" title="Link to this definition">¶</a></dt>

  395. <dd><p>The header to issue if the help output has a section for undocumented  commands

  396. (that is, there are <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_*()</span></code> methods without corresponding <code class="xref py py-meth docutils literal notranslate"><span class="pre">help_*()</span></code>

  397. methods).</p>

  398. </dd></dl>

  399. 

  400. <dl class="py attribute">

  401. <dt class="sig sig-object py" id="cmd.Cmd.ruler">

  402. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">ruler</span></span><a class="headerlink" href="#cmd.Cmd.ruler" title="Link to this definition">¶</a></dt>

  403. <dd><p>The character used to draw separator lines under the help-message headers.  If

  404. empty, no ruler line is drawn.  It defaults to <code class="docutils literal notranslate"><span class="pre">'='</span></code>.</p>

  405. </dd></dl>

  406. 

  407. <dl class="py attribute">

  408. <dt class="sig sig-object py" id="cmd.Cmd.use_rawinput">

  409. <span class="sig-prename descclassname"><span class="pre">Cmd.</span></span><span class="sig-name descname"><span class="pre">use_rawinput</span></span><a class="headerlink" href="#cmd.Cmd.use_rawinput" title="Link to this definition">¶</a></dt>

  410. <dd><p>A flag, defaulting to true.  If true, <a class="reference internal" href="#cmd.Cmd.cmdloop" title="cmd.Cmd.cmdloop"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cmdloop()</span></code></a> uses <a class="reference internal" href="functions.html#input" title="input"><code class="xref py py-func docutils literal notranslate"><span class="pre">input()</span></code></a> to

  411. display a prompt and read the next command; if false, <a class="reference internal" href="sys.html#sys.stdout" title="sys.stdout"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stdout.write()</span></code></a>

  412. and <a class="reference internal" href="sys.html#sys.stdin" title="sys.stdin"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stdin.readline()</span></code></a> are used. (This means that by importing

  413. <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">readline</span></code></a>, on systems that support it, the interpreter will automatically

  414. support <strong class="program">Emacs</strong>-like line editing  and command-history keystrokes.)</p>

  415. </dd></dl>

  416. 

  417. </section>

  418. <section id="cmd-example">

  419. <span id="id2"></span><h2>Cmd Example<a class="headerlink" href="#cmd-example" title="Link to this heading">¶</a></h2>

  420. <p>The <a class="reference internal" href="#module-cmd" title="cmd: Build line-oriented command interpreters."><code class="xref py py-mod docutils literal notranslate"><span class="pre">cmd</span></code></a> module is mainly useful for building custom shells that let a

  421. user work with a program interactively.</p>

  422. <p>This section presents a simple example of how to build a shell around a few of

  423. the commands in the <a class="reference internal" href="turtle.html#module-turtle" title="turtle: An educational framework for simple graphics applications"><code class="xref py py-mod docutils literal notranslate"><span class="pre">turtle</span></code></a> module.</p>

  424. <p>Basic turtle commands such as <a class="reference internal" href="turtle.html#turtle.forward" title="turtle.forward"><code class="xref py py-meth docutils literal notranslate"><span class="pre">forward()</span></code></a> are added to a

  425. <a class="reference internal" href="#cmd.Cmd" title="cmd.Cmd"><code class="xref py py-class docutils literal notranslate"><span class="pre">Cmd</span></code></a> subclass with method named <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_forward()</span></code>.  The argument is

  426. converted to a number and dispatched to the turtle module.  The docstring is

  427. used in the help utility provided by the shell.</p>

  428. <p>The example also includes a basic record and playback facility implemented with

  429. the <a class="reference internal" href="#cmd.Cmd.precmd" title="cmd.Cmd.precmd"><code class="xref py py-meth docutils literal notranslate"><span class="pre">precmd()</span></code></a> method which is responsible for converting the input to

  430. lowercase and writing the commands to a file.  The <code class="xref py py-meth docutils literal notranslate"><span class="pre">do_playback()</span></code> method

  431. reads the file and adds the recorded commands to the <a class="reference internal" href="#cmd.Cmd.cmdqueue" title="cmd.Cmd.cmdqueue"><code class="xref py py-attr docutils literal notranslate"><span class="pre">cmdqueue</span></code></a> for

  432. immediate playback:</p>

  433. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">cmd</span><span class="o">,</span> <span class="nn">sys</span>

  434. <span class="kn">from</span> <span class="nn">turtle</span> <span class="kn">import</span> <span class="o">*</span>

  435. 

  436. <span class="k">class</span> <span class="nc">TurtleShell</span><span class="p">(</span><span class="n">cmd</span><span class="o">.</span><span class="n">Cmd</span><span class="p">):</span>

  437.     <span class="n">intro</span> <span class="o">=</span> <span class="s1">&#39;Welcome to the turtle shell.   Type help or ? to list commands.</span><span class="se">\n</span><span class="s1">&#39;</span>

  438.     <span class="n">prompt</span> <span class="o">=</span> <span class="s1">&#39;(turtle) &#39;</span>

  439.     <span class="n">file</span> <span class="o">=</span> <span class="kc">None</span>

  440. 

  441.     <span class="c1"># ----- basic turtle commands -----</span>

  442.     <span class="k">def</span> <span class="nf">do_forward</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  443.         <span class="s1">&#39;Move the turtle forward by the specified distance:  FORWARD 10&#39;</span>

  444.         <span class="n">forward</span><span class="p">(</span><span class="o">*</span><span class="n">parse</span><span class="p">(</span><span class="n">arg</span><span class="p">))</span>

  445.     <span class="k">def</span> <span class="nf">do_right</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  446.         <span class="s1">&#39;Turn turtle right by given number of degrees:  RIGHT 20&#39;</span>

  447.         <span class="n">right</span><span class="p">(</span><span class="o">*</span><span class="n">parse</span><span class="p">(</span><span class="n">arg</span><span class="p">))</span>

  448.     <span class="k">def</span> <span class="nf">do_left</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  449.         <span class="s1">&#39;Turn turtle left by given number of degrees:  LEFT 90&#39;</span>

  450.         <span class="n">left</span><span class="p">(</span><span class="o">*</span><span class="n">parse</span><span class="p">(</span><span class="n">arg</span><span class="p">))</span>

  451.     <span class="k">def</span> <span class="nf">do_goto</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  452.         <span class="s1">&#39;Move turtle to an absolute position with changing orientation.  GOTO 100 200&#39;</span>

  453.         <span class="n">goto</span><span class="p">(</span><span class="o">*</span><span class="n">parse</span><span class="p">(</span><span class="n">arg</span><span class="p">))</span>

  454.     <span class="k">def</span> <span class="nf">do_home</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  455.         <span class="s1">&#39;Return turtle to the home position:  HOME&#39;</span>

  456.         <span class="n">home</span><span class="p">()</span>

  457.     <span class="k">def</span> <span class="nf">do_circle</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  458.         <span class="s1">&#39;Draw circle with given radius an options extent and steps:  CIRCLE 50&#39;</span>

  459.         <span class="n">circle</span><span class="p">(</span><span class="o">*</span><span class="n">parse</span><span class="p">(</span><span class="n">arg</span><span class="p">))</span>

  460.     <span class="k">def</span> <span class="nf">do_position</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  461.         <span class="s1">&#39;Print the current turtle position:  POSITION&#39;</span>

  462.         <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Current position is </span><span class="si">%d</span><span class="s1"> </span><span class="si">%d</span><span class="se">\n</span><span class="s1">&#39;</span> <span class="o">%</span> <span class="n">position</span><span class="p">())</span>

  463.     <span class="k">def</span> <span class="nf">do_heading</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  464.         <span class="s1">&#39;Print the current turtle heading in degrees:  HEADING&#39;</span>

  465.         <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Current heading is </span><span class="si">%d</span><span class="se">\n</span><span class="s1">&#39;</span> <span class="o">%</span> <span class="p">(</span><span class="n">heading</span><span class="p">(),))</span>

  466.     <span class="k">def</span> <span class="nf">do_color</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  467.         <span class="s1">&#39;Set the color:  COLOR BLUE&#39;</span>

  468.         <span class="n">color</span><span class="p">(</span><span class="n">arg</span><span class="o">.</span><span class="n">lower</span><span class="p">())</span>

  469.     <span class="k">def</span> <span class="nf">do_undo</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  470.         <span class="s1">&#39;Undo (repeatedly) the last turtle action(s):  UNDO&#39;</span>

  471.     <span class="k">def</span> <span class="nf">do_reset</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  472.         <span class="s1">&#39;Clear the screen and return turtle to center:  RESET&#39;</span>

  473.         <span class="n">reset</span><span class="p">()</span>

  474.     <span class="k">def</span> <span class="nf">do_bye</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  475.         <span class="s1">&#39;Stop recording, close the turtle window, and exit:  BYE&#39;</span>

  476.         <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Thank you for using Turtle&#39;</span><span class="p">)</span>

  477.         <span class="bp">self</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

  478.         <span class="n">bye</span><span class="p">()</span>

  479.         <span class="k">return</span> <span class="kc">True</span>

  480. 

  481.     <span class="c1"># ----- record and playback -----</span>

  482.     <span class="k">def</span> <span class="nf">do_record</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  483.         <span class="s1">&#39;Save future commands to filename:  RECORD rose.cmd&#39;</span>

  484.         <span class="bp">self</span><span class="o">.</span><span class="n">file</span> <span class="o">=</span> <span class="nb">open</span><span class="p">(</span><span class="n">arg</span><span class="p">,</span> <span class="s1">&#39;w&#39;</span><span class="p">)</span>

  485.     <span class="k">def</span> <span class="nf">do_playback</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>

  486.         <span class="s1">&#39;Playback commands from a file:  PLAYBACK rose.cmd&#39;</span>

  487.         <span class="bp">self</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

  488.         <span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">arg</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>

  489.             <span class="bp">self</span><span class="o">.</span><span class="n">cmdqueue</span><span class="o">.</span><span class="n">extend</span><span class="p">(</span><span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">()</span><span class="o">.</span><span class="n">splitlines</span><span class="p">())</span>

  490.     <span class="k">def</span> <span class="nf">precmd</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">line</span><span class="p">):</span>

  491.         <span class="n">line</span> <span class="o">=</span> <span class="n">line</span><span class="o">.</span><span class="n">lower</span><span class="p">()</span>

  492.         <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">file</span> <span class="ow">and</span> <span class="s1">&#39;playback&#39;</span> <span class="ow">not</span> <span class="ow">in</span> <span class="n">line</span><span class="p">:</span>

  493.             <span class="nb">print</span><span class="p">(</span><span class="n">line</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">file</span><span class="p">)</span>

  494.         <span class="k">return</span> <span class="n">line</span>

  495.     <span class="k">def</span> <span class="nf">close</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>

  496.         <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">file</span><span class="p">:</span>

  497.             <span class="bp">self</span><span class="o">.</span><span class="n">file</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

  498.             <span class="bp">self</span><span class="o">.</span><span class="n">file</span> <span class="o">=</span> <span class="kc">None</span>

  499. 

  500. <span class="k">def</span> <span class="nf">parse</span><span class="p">(</span><span class="n">arg</span><span class="p">):</span>

  501.     <span class="s1">&#39;Convert a series of zero or more numbers to an argument tuple&#39;</span>

  502.     <span class="k">return</span> <span class="nb">tuple</span><span class="p">(</span><span class="nb">map</span><span class="p">(</span><span class="nb">int</span><span class="p">,</span> <span class="n">arg</span><span class="o">.</span><span class="n">split</span><span class="p">()))</span>

  503. 

  504. <span class="k">if</span> <span class="vm">__name__</span> <span class="o">==</span> <span class="s1">&#39;__main__&#39;</span><span class="p">:</span>

  505.     <span class="n">TurtleShell</span><span class="p">()</span><span class="o">.</span><span class="n">cmdloop</span><span class="p">()</span>

  506. </pre></div>

  507. </div>

  508. <p>Here is a sample session with the turtle shell showing the help functions, using

  509. blank lines to repeat commands, and the simple record and playback facility:</p>

  510. <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>Welcome to the turtle shell.   Type help or ? to list commands.

  511. 

  512. (turtle) ?

  513. 

  514. Documented commands (type help &lt;topic&gt;):

  515. ========================================

  516. bye     color    goto     home  playback  record  right

  517. circle  forward  heading  left  position  reset   undo

  518. 

  519. (turtle) help forward

  520. Move the turtle forward by the specified distance:  FORWARD 10

  521. (turtle) record spiral.cmd

  522. (turtle) position

  523. Current position is 0 0

  524. 

  525. (turtle) heading

  526. Current heading is 0

  527. 

  528. (turtle) reset

  529. (turtle) circle 20

  530. (turtle) right 30

  531. (turtle) circle 40

  532. (turtle) right 30

  533. (turtle) circle 60

  534. (turtle) right 30

  535. (turtle) circle 80

  536. (turtle) right 30

  537. (turtle) circle 100

  538. (turtle) right 30

  539. (turtle) circle 120

  540. (turtle) right 30

  541. (turtle) circle 120

  542. (turtle) heading

  543. Current heading is 180

  544. 

  545. (turtle) forward 100

  546. (turtle)

  547. (turtle) right 90

  548. (turtle) forward 100

  549. (turtle)

  550. (turtle) right 90

  551. (turtle) forward 400

  552. (turtle) right 90

  553. (turtle) forward 500

  554. (turtle) right 90

  555. (turtle) forward 400

  556. (turtle) right 90

  557. (turtle) forward 300

  558. (turtle) playback spiral.cmd

  559. Current position is 0 0

  560. 

  561. Current heading is 0

  562. 

  563. Current heading is 180

  564. 

  565. (turtle) bye

  566. Thank you for using Turtle

  567. </pre></div>

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