Check Credit Card Number Validity in Python

Suppose we have a credit card number. We have to check whether the card number is valid or not. The card numbers have certain properties −

• It will start with 4, 5 and 6

• It will be 16 digits’ long

• Numbers must contain only digits

• It may have digits in four groups separated by '-'

• It must not use any other separator like space or underscore

• It must not have 4 or more consecutive same digits

So, if the input is like s = "5423-2578-8632-6589", then the output will be True

To solve this, we will follow these steps −

• if number of '-' in s is greater than 0, then
  • a := a list of parts separated by "-"
  • p:= 1
  • if size of a is not same as 4, then
    • p:= null
    • a:= blank list
  • for each b in a, do
    • if size of b is not same as 4, then
      • p:= null
      • come out from loop
• otherwise,
  • p := search a substring which is starting with 4 or 5 or 6 and remaining are numbers of 15 digits long
  • s := remove "-" from s
  • q := search substring where 4 or more consecutive characters are same
  • if p is not null and q is null, then
    • return True
  • otherwise,
    • return False

Example

Let us see the following implementation to get better understanding

import re

def solve(s):
   if s.count("-")>0:
      a = s.split("-")
      p=1
      if len(a)!=4:
         p=None
         a=[]
      for b in a:
         if len(b)!=4:
            p=None
            break
         else:
            p = re.search("[456][0-9]{15}",s)
         s = s.replace("-","")
         q = re.search(".*([0-9])\1{3}.*",s)

         if p!=None and q==None:
            return True
         else:
            return False

s = "5423-2578-8632-6589"
print(solve(s))

Input

"5423-2578-8632-6589"

Output

False