Using Tkinter widgets on child window

[Marbelous]

Yeah, strange but true: https://stackoverflow.com/questions/2855...x-elegance

It's also the reason why the OP is getting his: AttributeError: 'NoneType' object has no attribute 'insert'
Because on line 34 in his Second Window code he's in-lining the .place() function so now his self.Lb1 object is of type: None.

self.Lb1 = Listbox(self.bottom).place(x = 5, y = 140)

It's bitten me several times since I tend to favor compact, in-lined code.

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Quick example code:

from tkinter import * # Just quick example code.  Star imports are not a good idea!
master = Tk()

btn1 = Button(master, text="ONE")
btn1.pack()

btn2 = Button(master, text="TWO").pack()

print(type(btn1))
print(type(btn2))

<class 'tkinter.Button'>
<class 'NoneType'>

Process finished with exit code 0