def int_check(question):
    error = "Oops - please enter an integer."
    while True:
        try:
            response = int(input(question))
            return response
        except ValueError:
            print(error)


def not_blank(question):
    while True:
        response = input(question).strip()
        if response != "":
            return response
        print("Sorry, this can't be blank. Please try again.\n")


def string_check(question, valid_ans_list=('yes', 'no'), num_letters=1):
    while True:
        response = input(question).lower()
        for item in valid_ans_list:
            if response == item:
                return item
            elif response == item[:num_letters]:
                return item
        print(f"Please choose an option from {valid_ans_list}")


payment_ans = ('cash', 'credit')

c_price = 7.50
a_price = 10.50
s_price = 6.50

credit_sur = 0.05

while True:
    print()
    name = not_blank("Name: ")
    age = int_check("Age: ")

    if age < 12:
        print(f"{name} is too young.")
        continue

    elif 12 <= age < 16:
        ticket_price = c_price

    elif 16 <= age < 65:
        ticket_price = a_price

    elif 65 <= age < 121:
        ticket_price = s_price

    else:
        print(f"{name} is too old.")
        continue

    pay_method = string_check("Payment method (cash/credit): ", payment_ans, num_letters=2)

    if pay_method == "cash":
        sur = 0

    else:
        sur = ticket_price * credit_sur

    total_to_pay = ticket_price + sur

    print(f"{name}'s ticket cost ${ticket_price:.2f}, they paid by {pay_method}"
          f" so the surcharge is ${sur:.2f}\n"
          f"The total payable is ${total_to_pay:.2f}\n")