validating user input and loops

[Austin11]

So I am new to programming and I need to create a program that will allow the user to input how many bottles they collected over seven days. ie: Monday = 1, Tuesday = 5.... and then calculate the total number bottles collected and the amount of money they received (each bottle goes for 10 cents) I understand that part but when it comes to the validating the user's input I am lost. The invalid input gets stuck in a loop even when the user inputs a whole number. No error message is showing which makes it a bit hard to understand. Any help is greatly appreciated!

def is_valid_integer(input_string):
    try:
        val = int(input_string)
        is_valid = True
    except ValueError:
        is_valid = False
    return is_valid


def total_bottles_returned():
    input_string = ""

    mon = input("How many bottles did you return on Monday: ")
    is_valid = is_valid_integer(input_string)
    while not is_valid:
        mon = input("Nice try, please enter a whole number! ")
        is_valid = is_valid_integer(input_string)
    input_integer = int(mon)


    tue = input("How many bottles did you return on Tuesday: ")
    is_valid = is_valid_integer(input_string)
    while not is_valid:
        input_string = input("Nice try, please enter a whole number! ")
        is_valid = is_valid_integer(input_string)
    input_integer = int(input_string)


    wed = input("How many bottles did you return on Wednesday: ")
    is_valid = is_valid_integer(input_string)
    while not is_valid:
        input_string = input("Nice try, please enter a whole number! ")
        is_valid = is_valid_integer(input_string)
    input_integer = int(input_string)


    thu = input("How many bottles did you return on Thursday: ")
    is_valid = is_valid_integer(input_string)
    while not is_valid:
        input_string = input("Nice try, please enter a whole number! ")
        is_valid = is_valid_integer(input_string)
    input_integer = int(input_string)


    fri = input("How many bottles did you return on Friday: ")
    is_valid = is_valid_integer(input_string)
    while not is_valid:
        input_string = input("Nice try, please enter a whole number! ")
        is_valid = is_valid_integer(input_string)
    input_integer = int(input_string)


    sat = input("How many bottles did you return on Saturday: ")
    is_valid = is_valid_integer(input_string)
    while not is_valid:
        input_string = input("Nice try, please enter a whole number! ")
        is_valid = is_valid_integer(input_string)
    input_integer = int(input_string)


    sun = input("How many bottles did you return on Sunday: ")
    is_valid = is_valid_integer(input_string)
    while not is_valid:
        input_string = input("Nice try, please enter a whole number! ")
        is_valid = is_valid_integer(input_string)
    input_integer = int(input_string)

    return input_string, mon, tue, wed, thu, fri, sat, sun


def calculate_returned_bottles(mon, tue, wed, thu, fri, sat, sun):
    price_per_bottle = .10

    bottles_mon = int(mon) * price_per_bottle
    bottles_tue = int(tue) * price_per_bottle
    bottles_wed = int(wed) * price_per_bottle
    bottles_thur = int(thu) * price_per_bottle
    bottles_fri = int(fri) * price_per_bottle
    bottles_sat = int(sat) * price_per_bottle
    bottles_sun = int(sun) * price_per_bottle


    print("Monday pay out is: ", bottles_mon)
    print("Tuesday pay out is: ", bottles_tue)
    print("Wednesday pay out is: ", bottles_wed)
    print("Thursday pay out is: ", bottles_thur)
    print("Friday pay out is: ", bottles_fri)
    print("Saturday pay out is: ", bottles_sat)
    print("Sunday pay out is: ", bottles_sun)


    return bottles_mon,bottles_tue,bottles_wed,bottles_thur,bottles_fri,bottles_sat,bottles_sun


def calculate_final_bottle_price(bottles_mon, bottles_tue, bottles_wed, bottles_thur, bottles_fri ,bottles_sat, bottles_sun):
    monday = bottles_mon
    tuesday = bottles_tue
    wednesday = bottles_wed
    thursday = bottles_thur
    friday = bottles_fri
    saturday = bottles_sat
    sunday = bottles_sun

    final_bottle_price = (monday + tuesday + wednesday + thursday + friday + saturday + sunday)

    print("Total returned for the week: ", final_bottle_price)


def main():
    input_string, mon, tue, wed, thu, fri, sat, sun = total_bottles_returned()
    bottles_mon, bottles_tue, bottles_wed, bottles_thur, bottles_fri, bottles_sat, bottles_sun = calculate_returned_bottles(mon, tue, wed, thu, fri, sat, sun)
    calculate_final_bottle_price(bottles_mon, bottles_tue, bottles_wed, bottles_thur, bottles_fri ,bottles_sat, bottles_sun)


main()