def a(): print(x) y = 0 def b(): global x # x can't be change to 'nonlocal x, or error will arise' x = 1 y = 2 def c(): nonlocal y y = y + 1 def d(): nonlocal y y = y + 1 # print(y) a() d() c() print(y) b() # in python, to make it easier to learn, it uses indent, with no {} to declare variable in functions # to know how the variables from various functions, it uses global, nonlocal here in this example # by using global, variable x can go to and from the functions wherever 'global' is define # by using nonlocal, variable outside the upper level can be changed. Like the y in function d # function only runs with codes inside when it is called and point to the address it is located # to have no conflict between global and nonlocal, # nonlocal can only be used up to the 2 layers of functions, say function b, in this case