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

[Lee Harr]

On 2005-03-06, Stewart Midwinter <stewart.midwinter at gmail.com> 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?
>
> 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.
>
> 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?
>
> 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.
>

Depends a bit on who is updating who and which is
created first and which needs references to which.

Maybe like this...

> ---
> #objtest.py
>

class first:
    def __init__(self, a):
        self.a = a
        print 'a initialized to', self.a
        self.updater = second(self)

    def update(self, a='aa'):
        print 'initially, a is', self.a
        self.updater.do_update(a)
        print 'afterwards, a is', self.a

class second:
    def __init__(self, lst):
        self.lst = lst

    def do_update(self, a):
        self.lst.a = a


if __name__ == '__main__':
    lst = first('a')
    lst.update()

    # or ...
    dlg = second(lst)
    lst.update('aaa')