How can I move this class to separate file in python?

Question

Please have a look at the following code:

class Main:
    def __init__(self):
        # list to keep track of instances of Sub()
        self.sub_list = [] 
        # create instances of Sub()    
        self.a = Sub()
        self.b = Sub()
        # append instances to sub_list    
        self.sub_list.append(self.a)
        self.sub_list.append(self.b)


class Sub:
    # function to remove the instance from sub_list
    def remove_self(self):
        x.sub_list.remove(self)


x = Main()

# remove instances of Sub() from sub_list
x.a.remove_self()
x.b.remove_self()

My goal is to have objects with a method to delete themselves from a list in a different class, where they are created.

The above code works for this, but I don't like that I have to call the method by using x directly.

The main issue I'd like so solve, however, is that I can't figure out how to move the class Sub to a separate file, as I can't access sub_list anymore.

Is there a better way to do this?

Side note: I'm working on a project with PyQt, where Main is my MainWindow and Sub represents some UI elements that can be dynamically created and also closed. I'd like to keep all functionality within these elements if possible.

Answer 1

The ideal solution would be to not have a sub_list at all. It seems unnecessary since instances of Sub each get a field to themselves in your example. That being said, if you want to move Sub to a different file you can do it like so:

sub.py:

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

    def remove_self(self):
        self.parent.sub_list.remove(self)

And then in your main.py:

from sub import Sub
class Main:
    def __init__(self):
        self.sub_list = []  
        self.a = Sub(self)
        self.b = Sub(self)  
        self.sub_list.append(self.a)
        self.sub_list.append(self.b)

Then you can do:

x = Main()
x.a.remove_self()

or

x.sub_list[0].remove_self()

Or alternatively, and this is the approach I recommend, get rid of remove_self and add a new function to Main that takes care of removing Sub instances:

class Main:
    def __init__(self):
        self.sub_list = []  
        self.a = Sub(self)
        self.b = Sub(self)  
        self.sub_list.append(self.a)
        self.sub_list.append(self.b)

    def removeSub(self, index):
        self.sub_list.pop(index)

x = Main()
x.removeSub(0)