Very practical question

[Bruno Desthuilliers]

madpython a écrit :
> I've been doing an application with Tkinter widgets. Nothing really
> fancy just routine stuff. Though I have no problems with it by now I
> guess it would be reasonable to ask about a thing that's been bothering
> me a bit. Look at this piece of code:
> 
> class A(object):
>     def a(self):
>         return "a from A"
> 
> class B(object):
>     def interClassCall(self):
>         print globals()['c'].__dict__['a'].a()

Yuck. You're fired.

> class C(object):
>     def __init__(self):
>         self.a=A()
>         self.b=B()
>     def c(self):
>         self.b.interClassCall()
> 
> if __name__=="__main__":
>     c=C()
>     c.c()
> 
> What is another way to get data from method of another instance of a
> class?

Have a reference to that instance. Usually by one of the following method:
1/ create the C instance in the calling method
2/ have the C instance passed as an argument to the calling method
3/ have the C instance as an attribute of the B instance
4/ get the C instance from a module function (but then you have to solve 
how this module function itself gets the C instance, see above)

In your case, since it's the C instance that calls the B method that 
needs a reference to the C instance, just have the C instance pass 
itself to B:

class B(object):
     def interClassCall(self, c):
         print c.a.a()

class C(object):
     def __init__(self):
         self.a=A()
         self.b=B()
     def c(self):
         self.b.interClassCall(self)

Now, since B.interClassCall() doesn't need c, but the result of the call 
to c.a.a(), it would be better to directly pass that result:

class B(object):
     def interClassCall(self, something):
         print something

class C(object):
     def __init__(self):
         self.a=A()
         self.b=B()
     def c(self):
         self.b.interClassCall(self.a.a())


> Or maybe print globals()['c'].__dict__['a'].a() is perfectly
> normal. 

Definitively not. Not only is it a very complicated way to write a 
simple thing, but it's also totally defeating the whole point of using 
objects.

> I need your professional expertise.

It doesn't require any professional expertise to see what's wrong with 
your code. It's CS101.