Re: Can a method in one class change an object in another class?

[Kent Johnson]

Stewart Midwinter wrote:
I've got an app that creates an object in its main class (it also
creates a GUI).  My problem is that I need to pass this object, a
list, to a dialog that is implemented as a second class. I want to
edit the contents of that list and then pass back the results to the
first class.   So my question is, can a method in one class change an
object in another class?
Diez and Lee have shown you two ways to do this.
If the answer is no, I suppose I could pass in the list as an argument
when I create the second class, then return the contents of the list
when I end the methods in that second class.
This is almost what your example does, but you have made a small error. See 
below.
alternatively, I could make the list a global variable, then it would
be available to all classes.  I have a nagging feeling though that
global variables are to be avoided on general principle. Is this
correct?
Yes, it is correct.
Here's a simple example app that tries to have one class change the
object in another class.  It doesn't give the behaviour I want,
though.
---
#objtest.py
class first:
    def __init__(self):
        a = 'a'
        self.a = a
        print self.a
    def update(self):
        print 'initially, a is', self.a
        self.a = second(self.a)
The line above is creating an instance of second and assigning it to self.a. What you want to do is 
create an instance of second, *call* it, and assign the result to self.a. So you should have
          self.a = second(self.a)(self.a)

The self.a parameter passed to second is never used. If you change 
second.__init__ to
      def __init__(self):
          pass
then the call in update() will be
          self.a = second()(self.a)
Kent
        print 'afterwards, a is', self.a
class second:
    def __init__(self, a):
        pass
    def __call__(self, a):
        a = 'aa'
        return a
if __name__ == '__main__':
    app = first()
    app.update()
thanks,
--
Stewart Midwinter
[EMAIL PROTECTED]
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