Python3 global and nonlocal

test.py

a = 0 # global
def change1():
    a = 1 # nonlocal
    def change2():
        nonlocal a
        a = 3
    def change3():
        global a
        print('change3', a)
        a = 4
    change2()
    print(a) # output: 3
    change3() # output: change3 0
    print(a) # output: 3
change1()
print(a) # output: 4