Python global Keyword

Allows the conversion of a global read-only variable into a writeable variable.

Variables defined outside of a function or class are global but read-only, and are known as "constants". The global keyword tells Python that the variable is now read-writeable - it is not being treated as a constant.

Example

myConstant = 10  # This is a global read-only variable (a "constant")
    
class MyGlobalChanger
    def modifyMyConstant():
        global myConstant             # This allows us to change the "constant" value
        myConstant = myConstant + 5
            
print("myConstant is ", myConstant)
changer = MyGlobalChanger()
changer.modifyMyConstant()
print("myConstant is now ", myConstant)

Output

15

Notes: Use with caution!  Global variables usually should never be changed because this can cause side-effects when other code expects the global variable to behave like a constant.