The question is the cost of supporting it (assuming this is a problem needing fixing) as it has far reaching implications in all of the added complexity to all the abstractions layered on top of it.

I'm not making a good/bad argument that one is better than the other. The two languages have widely different usecases and rationale in the language design. But I'm not convinced C++ is (or can become) very Pythonic given the complexity it must support at all the basic levels.

Python 3 release date: 3 December 2008

C++11 release date: 12 August 2011

True, but in C++ the problem never existed.

This is fixed in Python 3 with the nonlocal keyword. In Python 2, the idiomatic work-around is to have x be list of one item:

    def f():
        x = [0]
        def add(amt):
            x[0] += amt
        add(10)
        return x[0]