parent reference issue python

Question

I have a wxPython application with some code like below. I want to set a value of an attribute of the class MyFrame, but I can't reference to it.
How can I make this code work?

class MyFrame1(wx.Frame):
    def __init__(self, *args, **kwds):
        wx.Frame.__init__(self, *args, **kwds)
        self.gauge_1 = wx.Gauge(self, -1)
        self.notebook_1=myNotebook(self, -1)

class myNotebook(wx.Notebook):
    def __init__(self, *args, **kwds):
        wx.Notebook.__init__(self, *args, **kwds)
        self.other_class_1=other_class()
        self.other_class_1.do_sth()

class other_class(object):
    def do_sth(self):
        gauge_1.SetValue(value) #doesn't work of course, how do I do this?

I don't feel like you could get an appropriate answer without first explaining what the role of other_class is? Is it really supposed to be a generic class that holds references to your MyFrame instance? What is the usage here? For all we know, MyFrame1 could have a global instance that could be accessed directly by an other_class instance. — jdi
– jdi, Commented Mar 10, 2012 at 0:06
I just realized what the other_class is after staring hard enough. Strange — jdi
– jdi, Commented Mar 10, 2012 at 0:11

jdi · Accepted Answer · 2012-03-10 00:34:19Z

I think its somewhat poor designer for a child UI element to have specific knowledge about its parent. Its a backwards design. Children should usually have some way of signaling or raising an event and letting the appropriate listener react. But, if this is really want you want to do, then you probably want to get the parent item and act on it directly...

Note: Don't do this approach. I'm illustrating why the design has issues...

First off, you can't even do it with the way the code is structured, because other_class has no reference to a parent. Its a generic instance. So you would have to do something like...

class other_class(object):

    def __init__(self, parent):
        self.parent = parent

And in your Notebook class...

class myNotebook(wx.Notebook):
    def __init__(self, *args, **kwds):
        wx.Notebook.__init__(self, *args, **kwds)
        # note here we pass a reference to the myNotebook instance
        self.other_class_1 = other_class(self)
        self.other_class_1.do_sth()

Then once your other_class now knows about its parent, you have to get the parent of the parent to have the MyFrame1 instance...

class other_class(object):

def __init__(self, parent):
    self.parent = parent

def do_sth(self, value):
    self.parent.GetParent().gauge_1.SetValue(value)

Do you see now why its a bad design? Multiple levels of objects have to assume knowledge of the parent structure.

I'm not up on my wxPython so I can't give you specifics, but here are some possible general approaches to consider:

Determine what the role of other_class really is. If its really meant to operate on children of your MyFrame1, then that functionality belongs under MyFrame1 so it can have knowledge of those members.
If other_class were a wx object, it could emit a wx.Event when the do_sth() method is called. You could bind that event at the MyFrame1 or Notebook level and do whatever work is needed in the handler.

Thank you for your clear and extensive answer. I know I shouldn't, but eventually I used the self.parent.GetParent() way. I already have too much code to completely redesign my program. I will however keep your hints in mind when writing future programs, which will then hopefully have a better design.

nitin · Accepted Answer · 2012-03-09 23:55:42Z

0

Try something like this:

class other_class(object):
     def __init__(self):
        self.g1=MyFrame1()
    def do_sth(self):
        self.g1.gauge_1.SetValue(value)

answered Mar 9, 2012 at 23:55

nitin

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