What is functionality of the '[recur]' in 'return (None, [lng])[recur]'

I've solved this challange on CodeWars in the other way, and now I'm learning from other solutions. One of them is:

# Recursive solution
def sqInRect(lng, wdth, recur = 0):
    if lng == wdth:
        return (None, [lng])[recur]            # If this is original function call, return None for equal sides (per kata requirement);
                                               # if this is recursion call, we reached the smallest square, so get out of recursion.
    lesser = min(lng, wdth)
    return [lesser] + sqInRect(lesser, abs(lng - wdth), recur = 1)

Could you please explain me what does this line mean: return (None, [lng])[recur] (the [recur] especially - I didn't see such a thing anywhere... is it an index, list or something? What functionality does it provide?). I know what does the code do, because mine does the same thing in another way, but I'm asking just about this sqare bracket in return Thanks a lot!

There's nothing magic about it; it's tuple indexing, plain and simple.

(None, [lng]) creates a tuple with two elements, and [recur] grabs the first or second element of this tuple depending on whether recur is 0 or 1.