Local variables cannot be modified. Global variables cannot be modified ？ How can it still run ？

answer ： because point += 2 amount to point = point + 2, This point Parameters received are 【 Positional arguments 】point

So it's equivalent to just 【 Local scope 】 Write an assignment statement .

def sum(point):
point += 2 # local variable
return point
point = 10 # Global variables
n = sum(5)
print(n)

It won't work like this ：

point = 4
def sum(name):
point = point + 2
return point
point = 10
n = sum(10)
print(n)

There is an error ：UnboundLocalError: local variable ‘point’ referenced before assignment. Translation is ： local variable point Quoted before assignment . in other words ：python hold point = point + 2 Medium point Used as a local variable , However, he was not assigned a value , Therefore, an error is reported , Why local variables don't use global variables point Well ？ This is because in the same row of assignment statements , Local variables cannot reference global variables , Will be python It is misunderstood as modifying the global variable value .