Validating credit card

[frequency]

Changed code to

def digit_sum(LIST):
    for i in range(len(LIST)):
      value = str(LIST[i])
      digits = [int(x) for x in value]
      credit_card.append(sum(digits))

def checker(s):
    list_of_numbers=[]
    string_to_use=""
    if("-" in s):
        list_of_numbers=s.split("-")
        for character in list_of_numbers:
            string_to_use+=character
        string_return=string_to_use
        string_to_use=""
        return string_return
    if(" " in s):
        list_of_numbers=s.split(" ")
        for character in list_of_numbers:
            string_to_use+=character
        string_return=string_to_use
        string_to_use=""
        return string_return
    if("," in s):
        list_of_numbers=s.split(",")
        for character in list_of_numbers:
            string_to_use+=character
        string_return=string_to_use
        string_to_use=""
        return string_return
    if("*" in s):
        list_of_numbers=s.split("*")
        for character in list_of_numbers:
            string_to_use+=character
        string_return=string_to_use
        string_to_use=""
        return string_return

    if("." in s):
        list_of_numbers=s.split(".")
        for character in list_of_numbers:
            string_to_use+=character
        string_return=string_to_use
        string_to_use=""
        return string_return
    else:return s

credit_card=[]
credit_card_sum=[]
credit_card_sum_digit=[]
credit_digits_sum=0

user1_input=input()
user_input=checker(user1_input)
while user1_input!="end" and user1_input!="END":
    user_input=checker(user1_input)
    if( not user_input.isdigit()):
        print("False")
    elif(user_input.isdigit() and len(user_input)>16):
        print("False")
    else:
        credit_card_int=[int(x) for x in user_input]
        if credit_card_int[0]<4 or credit_card_int[0]>=7:
          print ("False")
        else:
          for i in range(0,len(credit_card_int),2):
              credit_card_int[i] = credit_card_int[i]*2
          digit_sum(credit_card_int)
          for i in range(len(credit_card)):
            credit_digits_sum=credit_digits_sum+credit_card[i]
          if credit_digits_sum %10 ==0:
             print ("True")
          else:
            print ("False")
    user1_input=input()

but outputs wrong bool with input 54 97357 170632 130