Why can a function modify some arguments as perceived by the caller, but not others?

Question

I\'m trying to understand Python\'s approach to variable scope. In this example, why is f() able to alter the value of x, as perceived within

Answer 1

It´s because a list is a mutable object. You´re not setting x to the value of [0,1,2,3], you´re defining a label to the object [0,1,2,3].

You should declare your function f() like this:

def f(n, x=None):
    if x is None:
        x = []
    ...