• Inside the function definition (no matter where it happens), Python will automatically create that local variable if we do an assignment to a variable (and if we are not using the global keyword.)

# unbound local error

a = "Hello"

def change():
    print(a) #python create "a" local variable 
    a = 2  # a variable assignment
    
change() #local variable 'a' referenced before assignment

------------------------------------------------

UnboundLocalError: local variable 'a' referenced before assignment

理解Python的UnboundLocalError（Python的作用域） | 卡瓦邦噶！

全局变量报错：UnboundLocalError: local variable 'l' referenced before assignment | 菜鸟教程