cli: a command-line interface definer

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The wftk.cli class is really just some basic mechanisms for a CLI definition class. A CLI definition class must define a command dictionary and the actual command handlers.
class cli:
   """ Implements a CLI framework for handling action in either a GUI or a non-GUI context.

A more mature CLI implementation will have some introspection mechanisms, for the discovery and reporting of commands available and such, but at the moment I don't care about those. I'm going to ignore them completely. Let's cut to the chase and implement our "do" and "mode" methods. The mode is inanely simple. "Do" checks argument list lengths and hands off to the command method defined as the handler for the command. Easy as pie.

May 13, 2006: It now seems best to me to take an XML action or a command line string. If the latter is passed in, we'll ask the xmlobj library to convert it into an XML action for us. That parser is currently pretty naive, but later we can always make it better as needed.

January 1, 2007: I've added the "set_frame" method here because it makes a lot of sense in most WxPyWf applications. You can't pass the frame in when initializing the CLI, because the CLI has to be passed to the frame when it's created. So the frame will introduce itself to the CLI during its own initialization. For that to work, we have to know that every CLI will be able to deal with that. So it's logically right here. (This cleans up the individual CLI implementations, as well.)

Also today, I split out the "do" and "handle" functionality, so that I can ramify action objects and pass them around within the CLI list. Eventually this will take on frightening complexity.

   def mode(self, mode):
      self.mode = mode

   def do(self, context, action, obj=None):
      if type(action)==type(''):
         action = xmlobj(cmd=action)
         cmd = self.commands[action['command']]
         return None

      if int(action['parms']) < cmd[2] or (cmd[3] > 0 and int(action['parms']) > cmd[3]):    # TODO: eliminate the need for 'parms' as a command length value
         return [1, 'Usage: %s %s' % (cmd[0], cmd[4])]

      self.handle(context, cmd[1], action, obj=obj)

   def handle(self, context, cmd, action, obj=None): return cmd(context, action, obj)

   def set_frame(self, frame):
      self.frame = frame

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