What happens when you modify variables inside a function in Python

Recently writing Python encountered a problem with an internal variable using an external variable, now summarize it.

#!/usr/bin/env python

A = 100
def SU ():
A = a + 1
Print (a)

s = SU ()

#执行这段代码会报错 (if only the call is not modified will not be an error)

Change to:

#!/usr/bin/env python

A = 100
def SU ():
Global A
A = a + 1
Print (a)

s = SU ()

Summarize:

In Python's function and the global variable with the same name, if the value of the modified variable becomes a local variable,

A reference to the variable before it is modified will naturally occur without the definition of such an error,

If you are sure that you want to reference a global variable, and you want to modify it, you must add the Global keyword.

What happens when you modify variables inside a function in Python