[Python-ideas] Give nonlocal the same creating power as global

[João Matos]

Hello, 

I would like to suggest that nonlocal should be given the same creating 
power as global. 
If I do 
global a_var 
it creates the global a_var if it doesn't exist. 

I think it would be great that nonlocal maintained that power. 

This way when I do 
nonlocal a_var 
it would create a_var in the imediate parent environment, if it didn't 
exist. 

Without nonlocal creation powers I have to create global variables or local 
variables after master=Tk() (in the following example): 

from tkinter import StringVar, Tk 
from tkinter.ttk import Label 


def start_gui(): 
    def change_label(): 
        _label_sv.set('Bye Bye') 

    def create_vars(): 
        global _label_sv 

        _label_sv = StringVar(value='Hello World') 

    def create_layout(): 
        Label(master, textvariable=_label_sv).grid() 

    def create_bindings(): 
        master.bind('<Escape>', lambda _: master.destroy()) 
        master.bind('<Return>', lambda _: change_label()) 

    master = Tk() 

    create_vars() 
    create_layout() 
    create_bindings() 

    master.mainloop() 


if __name__ == '__main__': 
    start_gui() 


With nonlocal creation powers it would become a start_gui local variable 
(no global) but I could have a function to create the vars instead of 
having to add them after master=Tk(): 

from tkinter import StringVar, Tk 
from tkinter.ttk import Label 


def start_gui(): 
    def change_label(): 
        label_sv.set('Bye Bye') 

    def create_vars(): 
        nonlocal label_sv 

        label_sv = StringVar(value='Hello World') 

    def create_layout(): 
        Label(master, textvariable=label_sv).grid() 

    def create_bindings(): 
        master.bind('<Escape>', lambda _: master.destroy()) 
        master.bind('<Return>', lambda _: change_label()) 

    master = Tk() 

    create_vars() 
    create_layout() 
    create_bindings() 

    master.mainloop() 


if __name__ == '__main__': 
    start_gui() 



I know that I could also do it with OOP, but this way is more concise (OOP 
would add more lines and increase the lines length, which I personally 
dislike) 


This example is very simple, but if you imagine a GUI with several widgets, 
then the separation between vars, layout and bindings becomes useful for 
code organization. 


Best regards, 

João Matos 

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