symbian-qemu-0.9.1-12/python-2.6.1/Doc/library/cmd.rst
author johnathan.white@2718R8BGH51.accenture.com
Mon, 08 Mar 2010 18:45:03 +0000
changeset 46 b6935a90ca64
parent 1 2fb8b9db1c86
permissions -rw-r--r--
Modify framebuffer and NGA framebuffer to read screen size from board model dtb file. Optimise memory usuage of frame buffer Add example minigui application with hooks to profiler (which writes results to S:\). Modified NGA framebuffer to run its own dfc queue at high priority


:mod:`cmd` --- Support for line-oriented command interpreters
=============================================================

.. module:: cmd
   :synopsis: Build line-oriented command interpreters.
.. sectionauthor:: Eric S. Raymond <esr@snark.thyrsus.com>


The :class:`Cmd` class provides a simple framework for writing line-oriented
command interpreters.  These are often useful for test harnesses, administrative
tools, and prototypes that will later be wrapped in a more sophisticated
interface.


.. class:: Cmd([completekey[, stdin[, stdout]]])

   A :class:`Cmd` instance or subclass instance is a line-oriented interpreter
   framework.  There is no good reason to instantiate :class:`Cmd` itself; rather,
   it's useful as a superclass of an interpreter class you define yourself in order
   to inherit :class:`Cmd`'s methods and encapsulate action methods.

   The optional argument *completekey* is the :mod:`readline` name of a completion
   key; it defaults to :kbd:`Tab`. If *completekey* is not :const:`None` and
   :mod:`readline` is available, command completion is done automatically.

   The optional arguments *stdin* and *stdout* specify the  input and output file
   objects that the Cmd instance or subclass  instance will use for input and
   output. If not specified, they will default to :data:`sys.stdin` and
   :data:`sys.stdout`.

   If you want a given *stdin* to be used, make sure to set the instance's
   :attr:`use_rawinput` attribute to ``False``, otherwise *stdin* will be
   ignored.

   .. versionchanged:: 2.3
      The *stdin* and *stdout* parameters were added.


.. _cmd-objects:

Cmd Objects
-----------

A :class:`Cmd` instance has the following methods:


.. method:: Cmd.cmdloop([intro])

   Repeatedly issue a prompt, accept input, parse an initial prefix off the
   received input, and dispatch to action methods, passing them the remainder of
   the line as argument.

   The optional argument is a banner or intro string to be issued before the first
   prompt (this overrides the :attr:`intro` class member).

   If the :mod:`readline` module is loaded, input will automatically inherit
   :program:`bash`\ -like history-list editing (e.g. :kbd:`Control-P` scrolls back
   to the last command, :kbd:`Control-N` forward to the next one, :kbd:`Control-F`
   moves the cursor to the right non-destructively, :kbd:`Control-B` moves the
   cursor to the left non-destructively, etc.).

   An end-of-file on input is passed back as the string ``'EOF'``.

   An interpreter instance will recognize a command name ``foo`` if and only if it
   has a method :meth:`do_foo`.  As a special case, a line beginning with the
   character ``'?'`` is dispatched to the method :meth:`do_help`.  As another
   special case, a line beginning with the character ``'!'`` is dispatched to the
   method :meth:`do_shell` (if such a method is defined).

   This method will return when the :meth:`postcmd` method returns a true value.
   The *stop* argument to :meth:`postcmd` is the return value from the command's
   corresponding :meth:`do_\*` method.

   If completion is enabled, completing commands will be done automatically, and
   completing of commands args is done by calling :meth:`complete_foo` with
   arguments *text*, *line*, *begidx*, and *endidx*.  *text* is the string prefix
   we are attempting to match: all returned matches must begin with it. *line* is
   the current input line with leading whitespace removed, *begidx* and *endidx*
   are the beginning and ending indexes of the prefix text, which could be used to
   provide different completion depending upon which position the argument is in.

   All subclasses of :class:`Cmd` inherit a predefined :meth:`do_help`. This
   method, called with an argument ``'bar'``, invokes the corresponding method
   :meth:`help_bar`.  With no argument, :meth:`do_help` lists all available help
   topics (that is, all commands with corresponding :meth:`help_\*` methods), and
   also lists any undocumented commands.


.. method:: Cmd.onecmd(str)

   Interpret the argument as though it had been typed in response to the prompt.
   This may be overridden, but should not normally need to be; see the
   :meth:`precmd` and :meth:`postcmd` methods for useful execution hooks.  The
   return value is a flag indicating whether interpretation of commands by the
   interpreter should stop.  If there is a :meth:`do_\*` method for the command
   *str*, the return value of that method is returned, otherwise the return value
   from the :meth:`default` method is returned.


.. method:: Cmd.emptyline()

   Method called when an empty line is entered in response to the prompt. If this
   method is not overridden, it repeats the last nonempty command entered.


.. method:: Cmd.default(line)

   Method called on an input line when the command prefix is not recognized. If
   this method is not overridden, it prints an error message and returns.


.. method:: Cmd.completedefault(text, line, begidx, endidx)

   Method called to complete an input line when no command-specific
   :meth:`complete_\*` method is available.  By default, it returns an empty list.


.. method:: Cmd.precmd(line)

   Hook method executed just before the command line *line* is interpreted, but
   after the input prompt is generated and issued.  This method is a stub in
   :class:`Cmd`; it exists to be overridden by subclasses.  The return value is
   used as the command which will be executed by the :meth:`onecmd` method; the
   :meth:`precmd` implementation may re-write the command or simply return *line*
   unchanged.


.. method:: Cmd.postcmd(stop, line)

   Hook method executed just after a command dispatch is finished.  This method is
   a stub in :class:`Cmd`; it exists to be overridden by subclasses.  *line* is the
   command line which was executed, and *stop* is a flag which indicates whether
   execution will be terminated after the call to :meth:`postcmd`; this will be the
   return value of the :meth:`onecmd` method.  The return value of this method will
   be used as the new value for the internal flag which corresponds to *stop*;
   returning false will cause interpretation to continue.


.. method:: Cmd.preloop()

   Hook method executed once when :meth:`cmdloop` is called.  This method is a stub
   in :class:`Cmd`; it exists to be overridden by subclasses.


.. method:: Cmd.postloop()

   Hook method executed once when :meth:`cmdloop` is about to return. This method
   is a stub in :class:`Cmd`; it exists to be overridden by subclasses.

Instances of :class:`Cmd` subclasses have some public instance variables:


.. attribute:: Cmd.prompt

   The prompt issued to solicit input.


.. attribute:: Cmd.identchars

   The string of characters accepted for the command prefix.


.. attribute:: Cmd.lastcmd

   The last nonempty command prefix seen.


.. attribute:: Cmd.intro

   A string to issue as an intro or banner.  May be overridden by giving the
   :meth:`cmdloop` method an argument.


.. attribute:: Cmd.doc_header

   The header to issue if the help output has a section for documented commands.


.. attribute:: Cmd.misc_header

   The header to issue if the help output has a section for miscellaneous  help
   topics (that is, there are :meth:`help_\*` methods without corresponding
   :meth:`do_\*` methods).


.. attribute:: Cmd.undoc_header

   The header to issue if the help output has a section for undocumented  commands
   (that is, there are :meth:`do_\*` methods without corresponding :meth:`help_\*`
   methods).


.. attribute:: Cmd.ruler

   The character used to draw separator lines under the help-message headers.  If
   empty, no ruler line is drawn.  It defaults to ``'='``.


.. attribute:: Cmd.use_rawinput

   A flag, defaulting to true.  If true, :meth:`cmdloop` uses :func:`raw_input` to
   display a prompt and read the next command; if false, :meth:`sys.stdout.write`
   and :meth:`sys.stdin.readline` are used. (This means that by importing
   :mod:`readline`, on systems that support it, the interpreter will automatically
   support :program:`Emacs`\ -like line editing  and command-history keystrokes.)