(Easy ??) question about class definition

[Gordon McMillan]

Gregoire Welraeds writes:
> 
> I think the problem I have is common in OOP... but I don't have any
> beginning of solution.

That's because Python makes it too easy ;-).
 
> I got the following problem. Imagine i want to manage a menu. So I define
> 2 classes. First one is the class menu and is basicly a list of entry. The
> second is the item class representing each menu entry. When an item of my
> menu is selected, I want to execute some action... The action I want to
> perform is different for each item. So I get the following
> 
> class entry:
> 	def __init__(self, name, action):
> 		self.name= name
> 		self.action= action
> 	def selected():
> 		exec(self.action)
> 	[some methods]

Not quite. Change that to:
  def selected(self):
    self.action()

Now the actions can be functions:

def action1():
  print "action1"

e1 = entry("First", action1)
 
 or bound methods:

class A:
  ....
  def action(self):
    print "A.action"

a = A()
e2 = entry("Second", a.action)

That's all there is to it.

> class menu:
> 	def __init__(self, name):
> 		self.name= name
> 		self.list=[]
> 	[some methods]
> ...
> 
> Now self.action is a reference to something I have to define elsewhere. It
> could be a separate function... but then, the function is not bound to a
> class as method are and everybody can use it. And I don't want to have
> each action to be define in the class. 
> thus the problem is that each action i bound with an instance of the class
> item.
> I know there are some solutions in Design Pattern but I don't know howto
> implement this in Python.
> 
> thanks for your answer.
> 
> --
> Life is not fair
> But the root password helps
> --
> 
> Gregoire Welraeds
> greg at perceval.be
> Perceval Development team
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- Gordon