Modify the function of global variables

# Share data between functions, global variable modifications 
    # 1, the use of global variables 
    # 2, the return value of 
a global variable is a variable type (list, dict, set), without modifying the global variable declaration globle function in 

g_num = 1 # defined global variable 
DEF modify_value1 (): 
    global g_num # modify global variables the same variables are declared first, and then modify 
    g_num = 10 # use without first global declaration, a local variable is defined 

print ( 'before modification:', g_num) 
modify_value1 ( ) # call function to modify global variables 
print ( 'modified:', g_num) 

DEF modify_value2 (): 
    global g_num 
    g_num = 20 is 
    return g_num 

DEF Show (): 
    value = modify_value2 () 
    Print (value) 

Show ()