Question

I’m writing a small program that prints a menu screen with a list of options. If you choose one of the options, the screen is cleared and you’re taken to the next menu.

Right now, I’ve made a base Menu class and given it a method draw() which draws the options. I then want to add a another method handle_options() which takes user input and then whisks the user off to the appropriate choice.

At the moment, I am creating a series of subclasses like class MainMenu(Menu) and class OptionsMenu(Menu). When handle_options() is looping, I’ll create an instance of the appropriate Menu class, and draw it, then loop into option choices.

But the thing is, I don’t want to have to define this handle_options() method for each variant of Menu. So I ask:

a) Is there a design pattern or better way of doing this kind of thing I can learn from?

b) Can I use something like getattr(self, "myfunc")() to call a function name I have stored in an array, so I can genericise the handle_options() method and define it in the base Menu class, rather than for each subclass?

tl;dr – What kinds of examples or patterns can be used to build a simple text-based menu system?

Answer 1

An alternative to defining handle_options for every subclass of Menu is to define a dict that maps an option to a function call:

class Menu(object):
   def __init__(self):
      # Ideally, self._options would be an empty dict for the base class.
      # This is just for the sake of example.
      self._options = {'a': self.optionA,
                       'b': self.optionB}

   def handle_options(self, option):
      if option not in self._options:
         print "Invalid option"
         # re-draw
         return

      self._options[option]()

   def optionA(self):
      print "option A"

   def optionB(self):
      print "option B"

Now your subclasses simply have to redefine self._options and provide the appropriate methods associated with each option:

class SubMenu(Menu):
   def __init__(self):
      Menu.__init__(self)

      self._options = {'c': self.optionC,
                       'd': self.optionD}

   def optionC(self):
      # ...

   def optionD(self):
      # ...

You can also expand on self._options to provide text description, for example, so your draw function can simply iterate through the options printing each one. Take a look at how to use argparse to infer a good design.