text: def luhn_checksum(number):
      def digits_of(n):
          return [int(d) for d in str(n)]
  
      digits = digits_of(number)
      odd_digits = digits[-1::-2]
      even_digits = digits[-2::-2]
      checksum = 0
      checksum += sum(odd_digits)
      for d in even_digits:
          checksum += sum(digits_of(d * 2))
      return checksum % 10
  
  
  def calculate_luhn(partial_number):
      """
      Generates the Checksum using Luhn's algorithm
      """
      check_digit = luhn_checksum(int(partial_number) * 10)
      return check_digit if check_digit == 0 else 10 - check_digit
  