Python functions

def add_numbers(x,y,z=None):
    if (z==None):
        return x+y
    else:
        return x+y+z
 
print(add_numbers(1, 2))
print(add_numbers(1, 2, 3))

def add_numbers(x, y, z=None, flag=False):
    if (flag):
        print('Flag is true!')
    if (z==None):
        return x + y
    else:
        return x + y + z
 
print(add_numbers(1, 2, flag=True))