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')

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

    if age < 12:
        print(f"{name} is too young.")
        continue
    elif age > 120:
        print(f"{name} is too old.")
        continue

    pay_method = string_check("Payment method (cash/credit): ", payment_ans, num_letters=2)
    print(f"{name} has bought a ticket ({pay_method}).")