Tkinter: using return for widgets

Question

So, I have been having trouble figuring out what does return do when used for tkinter widgets

here are 3 blocks of code that have the same result, and I wasn't sure what their difference is and whether they differ in performance, and finally, which one is the standard approach

1

import tkinter as tk
class App:
    def __init__(self):
        window = tk.Tk()
        self.label_in_window(window, text = "hello world!")
        window.mainloop()

    def label_in_window(self, parent, text):
        return tk.Label(parent, text = text).pack()
App()

2

import tkinter as tk
class App:
    def __init__(self):
        window = tk.Tk()
        self.label_in_window(window, text = "hello world!")
        window.mainloop()

    def label_in_window(self, parent, text):
        tk.Label(parent, text = text).pack()
        return
App()

3

import tkinter as tk
class App:
    def __init__(self):
        window = tk.Tk()
        self.label_in_window(window, text = "hello world!")
        window.mainloop()

    def label_in_window(self, parent, text):
        tk.Label(parent, text = text).pack()
App()

Does this answer your question? [Tkinter: AttributeError: NoneType object has no attribute ](https://stackoverflow.com/questions/1101750/tkinter-attributeerror-nonetype-object-has-no-attribute-attribute-name) — TheLizzard, Aug 23 '21 at 10:27
If you want to return the widget, none of the methods above work. You should instead use `label = tk.Label(...); label.pack(); return label` — TheLizzard, Aug 23 '21 at 10:28
Actually I don't want to return the widget, I just want it to show the widget — Ali Keykha, Aug 23 '21 at 10:34

score 3 · Answer 1 · answered Aug 23 '21 at 10:35

In the first example you used:

return tk.Label(parent, text=text).pack()

Which creates a label, calls .pack() on the label. It returns whatever .pack() returns (which is None). For more info please read this. So it's identical to:

tk.Label(parent, text=text).pack()
return None

The second example uses:

tk.Label(parent, text = text).pack()
return

Which creates the label. The return is the same as return None.

In the third example uses:

tk.Label(parent, text=text).pack()

Which creates a label then returns None.

Therefore, all the examples that you have shown are exactly the same. They all create a label and return None.

PS: If you use from dis import dis and then dis(App.label_in_window), you will see the decompiled bytecode, which is what python actually uses to run your code.

TheEagle · Accepted Answer · 2021-08-23T10:45:57.413

Per code answer:

does not make sense, because you are returning something, but then throwing the returned result away.
you can remove the return statement because all functions by default return None, and a return statement without a value also returns None. This then makes 2. and 3. equal.
If you just want to put the creation of widgets into a separate function, use the 3rd code.

Anyways, all the returns do not make sense in your code, because they will always return None. Guess why ? No ? I'll explain it. It's because of this line:

tk.Label(parent, text = text).pack()

First you create a tk.Label object. Then, you call its pack method which of course returns None. So in the end, you have not a tk.Label, but a None. To change this, you should first assign your tk.Label object to a variable, then call the pack method of the variable, then return the variable:

    def label_in_window(self, parent, text):
        label = tk.Label(parent, text=text)
        label.pack()
        return label

But, if you are not planning to use the label later (set a new text, for example), it doesn't make sense to return the label. If you do want to use it later, the standard approach in a class would be to assign the label to an attribute of your class. Also, you should move the window.mainloop out of the class, and functions / methods should be named after what they do, not which result they produce:

import tkinter as tk
class App:
    def __init__(self):
        self.window = tk.Tk()
        self.add_label(self.window, text="hello world!")

    def add_label(self, parent, text):
        self.label = tk.Label(parent, text=text)
        self.label.pack()

app = App()
app.window.mainloop()

Tkinter: using return for widgets

2 Answers2