Main method to call a custom object in Python

Question

I was trying to fix something related to what an object returns when you use an object as an argument.

For example, I have a custom object and I want to use it as a parent for another tkinter widget, so I need to return a tkinter object to place the new tkinter object into my custom object, but my custom object returns that is an object of a custom class.

I can explain this much better on code:

class CustomFrame(object):
    def __init__(self,**args):
        #code that works

        #The next is an external object that have a variable that I need to call externally.
        #The variable is "interior"
        self.externalobject = anotherobject('random')

cfr1 = CustomFrame()

label1 = Label(cfr1)

Now I want to use the "self.externalobject.interior" as the parent for label1 But I want to make it friendly just calling "cfr1" instead of "self.externalobject.interior"

I know that if I use the call method and I return the value that I need it will work if I pass "cfr1" as a function, but I want to make it the more Pythonic as possible.

So I need to know if there's another special method or something to modify what it returns.

EDIT: So, this is part of the code I am using:

This is the code of the vertical scrolled frame (not my code).

class VerticalScrolledFrame(Frame):
    """A pure Tkinter scrollable frame that actually works!
    * Use the 'interior' attribute to place widgets inside the scrollable frame
    * Construct and pack/place/grid normally
    * This frame only allows vertical scrolling

    """
    def __init__(self, parent, bg, *args, **kw):
        Frame.__init__(self, parent, *args, **kw)            

        # create a canvas object and a vertical scrollbar for scrolling it
        vscrollbar = Scrollbar(self, orient=VERTICAL)
        canvas = Canvas(self, bd=0, highlightthickness=0,
                        yscrollcommand=vscrollbar.set,bg=bg)
        vscrollbar.config(command=canvas.yview)
        canvas.pack(side=LEFT, fill=BOTH, expand=TRUE)

        # reset the view
        canvas.xview_moveto(0)
        canvas.yview_moveto(0)

        # create a frame inside the canvas which will be scrolled with it
        self.interior = interior = Frame(canvas,bg=bg)
        interior_id = canvas.create_window(0, 0, window=interior,
                                           anchor=NW)

        a = Frame(self.interior,height=10,bg=dynamicBackground())
        a.pack()

        def canvasscroll(event):
            canvas.yview('scroll',int(-1*(event.delta/120)), "units")

        def _configure_canvas(event):
            a.configure(height=10)
            a.update()
            mylist = interior.winfo_children()
            for i in mylist:
                lasty=i.winfo_height()+i.winfo_y()
            a.configure(height=lasty)
            if interior.winfo_reqwidth() != canvas.winfo_width():
                # update the inner frame's width to fill the canvas
                canvas.itemconfigure(interior_id, width=canvas.winfo_width())
            if canvas.winfo_height()<lasty:
                vscrollbar.pack(fill=Y, side=RIGHT, expand=FALSE)
                canvas.config(scrollregion=(0,0,0,lasty))
                canvas.bind_all("<MouseWheel>", canvasscroll)
            else:
                canvas.unbind_all("<MouseWheel>")
                try:
                    vscrollbar.pack_forget()
                except:
                    pass
                canvas.config(scrollregion=(0,0,0,0))


        canvas.bind('<Configure>', _configure_canvas)

And this is the code for my custom object:

class UtilityPanel(object):
    def __init__(self,parent='*',title='Main Title',state='normal',bg='red'):
        super().__init__()
        if parent != '*':
            self.parent=parent
        else:
            raise TypeError('You must specify a parent for this widget.')
        self.title=title

        global subpanels

        if len(subpanels) == 0:
            self.panelid = 'sp-1'
            subpanels.append('sp-1')
        else:
            self.panelid = 'sp-'+str(int(subpanels[-1].split('-')[1])+1)
            subpanels.append(self.panelid)

        self.panel = VerticalScrolledFrame(self.parent,bg=bg,width=600,height=200,name=self.panelid)

    def __call__(self,name):
        return(self.panel.interior)

    def pack(self):
        self.panel.place(x=300)
        global activepanel
        activepanel = self.panelid

So, if i pass the argument like label1 = Label(cfr1.panel.interior) it works, but I want it to make it work just passing cfr1 as an argument.

Answer 1

I think I understand the issue the OP is having here. They are unable to use the frame as the container for their label and that is because they are missing super() and need to inherit from Frame.

Change this:

class CustomFrame(object):
    def __init__(self,**args):

To this:

class CustomFrame(Frame):
    def __init__(self,**args):
        super().__init__()

And you should be able to use the customer frame as the container for your label.

Based on your comments below try this:

class CustomFrame(anotherobject):
    def __init__(self,**args):
        super().__init__()

This should inherit all methods and attributes of that object.

Answer 2

You are trying to implicitly cast/coerce one type of object to another.

If you want to be "pythonic", recall,

>>> import this
The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
...

Implicitly doing things can cause trouble.

I see nothing wrong with using the call magic function to get the attribute you want, or start looking at properties and decorators.

There's a full list of magic methods here

Answer 3

You could probably achieve what you want if you created your own custom subclass of tk.Label that basically does the unpacking for you.

(Disclaimer: I have never used tkinter, so I cannot tell if this actually works in the context of that framework. This example is merely to demonstrate the concept I am trying to outline here.)

class CustomLabel(tk.Label):

    def __init__(self, master, **options):
        if isinstance(master, CustomFrame):
            master = master.externalobject.interior
        super().__init__(master=master, **options)

With that you should be able to use CustomLabel(cfr1).

However, I strongly support the message that @doctorlove conveys in their answer. IMHO, the most pythonic way would indeed be Label(cfr1.externalobject.interior), your suggested approach using __call__ or a property inside CustomFrame that provides a shortcut to externalobject.interior:

@property
def interior(self):
    return self.externalobject.interior

which you would use like so Label(crf1.interior)