While-loops in Python

while.py

def foo(x, y):
    current = x + y
    while (current < 100):
        current = current + x + y
        print(current)
    print("loop finished")


foo(10, 10)

def get_yn ():
    response = ""
    while (response != "y" and response != "n"):
        response = input("Type y or n to continue: ")
    return response

valid = False
while (not valid):
    s = input ("Enter a password: ")
    valid = (len(s) == 5 and s[:2] == "xy")


# 􏰀 A.xyz
# 􏰀 B. abcxy
# 􏰀 C. xyabc
# 􏰀 D. More than one of the above passwords get us out of the loop
# 􏰀 E. None; the loop never executes and no passwords are obtained

def double_money(deposit):
    years = 0
    while ():
        #...
        year = year + 1
    return years