Calling a method which uses variables from another method in a class

Question

I'm writing a script in Maya and trying to assign a variable inside another method instead of inside __init__ like we normally do. I put my window commands inside the __init__ so when a new instance is initialized, if we assign variables inside __init__ it will run all the way through without assigning the variables the value I want.

For example:

    def __init__(self, windowID = 'selectsomething', title = 'select something'):
        self.windowID = windowID
        self.title = title

        if cmds.window(self.windowID, exists = True):
            cmds.deleteUI(self.windowID)
                    
        myWindow = cmds.window(self.windowID, title = self.title)
        cmds.rowColumnLayout(numberOfColumns = 2, columnWidth = [(1, 300), (2, 100)],
                             columnAttach = [1, 'left', 10], columnSpacing = [1, 10],
                             rowSpacing = [1, 5])
        cmds.button(label = "Apply", command = self.applyButton) #it should print out selected object
        cmds.button(label = "Cancel", command = self.cancelButton)
        cmds.showWindow(myWindow)

        #now for example if I have a sel variable to store selected objects, it would actually return nothing cuz the code ran all the way through and didnt wait for me to select what I needed
        sel = cmds.ls(selection = True) #this will return nothing

My solution is to assign variables inside the applyButton method, which will store what I selected. I found it's a bit weird to call a method which uses a variable from another method from that method itself.

For example:

class Abc:
    def func(*arg):
        print(self.var)
    
    def var(self):
        self.var = 1
        self.func()
        
abc = Abc()
abc.var()

For now the code runs, but doesn't it sound a bit weird to call the func method which uses the variable from var method from var method itself?

I haven't seen anyone do it. I mean without class, a variable assigned inside a function stays inside that function and we can only use it with return . But it looks like in class we can make any inside-method-variable global by adding self. before it?

My friend also said we can use @property in this case but I don't think I figured it out yet.

Answer 1

You need to be aware that data attributes are implicitly a member of the class and can therefore be used by any method in the same class after they have been assigned somewhere.

From the Python documentation :

Data attributes need not be declared; like local variables, they spring into existence when they are first assigned to.

While your example will work (if you call Abc.var() before Abc.func() ), it would IMHO be better style to initialize the variable at class level like this (note that I call it val to avoid confusion with the method name):

class Abc:
    val = 0

    def func(self, *arg):
        print(self.val)

    def var(self):
        self.val = 1
        self.func()

The purpose of the self keyword is nicely explained here and here .

Also note that initializing an attribute inside the __init__ method will bind this attribute to a class instance, whereas initializing it outside of the __init__ method will bind it to the class itself, which is a different thing (see this discussion ).