Validating credit card

[frequency]

Yea,sorry for this. I keep on making many versions of the code so i keep experimenting. Take my code

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):
  return s.replace(' ','').replace('-','')
        
 
credit_card=[]
credit_card_sum=[]
credit_card_sum_digit=[]
credit_digits_sum=0    
 
user_input=input()
user_input = checker(user_input) # <===== HERE
while user_input!="end" and user_input!="END":  
     
   credit_card_str=str(user_input)
    
   credit_card_int=[int(x) for x in credit_card_str]
   if credit_card_int[0]<4 or credit_card_int[0]>=7:
       
     print ("False")
   else:
    for i in range(len(credit_card_int)):
      if not (i% 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 % 2 ==0:
     print ("True")
    else:
     print ("False")
   user_input=input()
   user_input = checker(user_input) # <===== HERE