def string_check(question, valid_ans_list=('yes', 'no'),
                 num_letter=1):
    """checks the users enter the full word or the first letter of a word
    from a list of responces"""

    while True:
        response = input(question).lower()


        for item in valid_ans_list:


            #checks if the response is the entire word
            if response == item:
                return item

            #checks if the responce is the first letter
            elif response == item [:num_letter]:
                return item

        print(f"please choose an option from {valid_ans_list}")

#main routine
payment_list = ('cash','credit')
want_instuction = string_check("do you want instructions? ")
print(f"you chose {want_instuction}")
payment_method = string_check("payment method", payment_list,2)
print(f"you chose {payment_method}")