Python中的变量作用域存在问题

x = 10

def func():
    global x
    x = 20
    print(x)

func()
print(x)

20
20

def func(x):
    x = 20
    print(x)

x = 10
func(x)
print(x)

20
10

def func():
    x = 20
    return x

x = 10
x = func()
print(x)

20

def outer():
    x = 10

    def inner():
        nonlocal x
        x = 20
        print(x)

    inner()
    print(x)

outer()

20
20