函数中的Python3变量

Question

def a():
    b = 1
    def x():
        b -= 1
    if something is something:
        x()
a()

What im wanting here is to change b from a() in x() I have tried using;

def a():
    b = 1
    def x():
        global b
        b -= 1
    if something is something:
        x()

a()

But this, as I expected, this told me global b is not defined.

b needs to change after x() is has run and if x() is called a second time b needs to be what x() set it to - 0 not what it was originally set to in a() - 1.

Answer 1

In order to alter the value of a variable defined in a containing scope, use nonlocal . This keyword is similar to intent to global (which indicates the variable should be considered to be the binding in the global scope).

So try something like:

def a():
    b = 1
    def x():
        # indicate we want to be modifying b from the containing scope
        nonlocal b
        b -= 1
    if something is something:
        x()

a()

Answer 2

This should work:

def a():
    b = 1
    def x(b):
        b -= 1
        return b
    b = x(b)
    return b
a()