code: def cmd_crack_luhn(number):
      
  
      number = number.replace('-', '')
      unknown_count = number.count('x')
  
      if not number.replace('x', '').isdigit():
          print('Invalid format. Please, read the documentation.', file=sys.stderr)
          sys.exit(1)
  
      for n in range(10 ** unknown_count):
          candidate = number
          for item in '{:0{count}}'.format(n, count=unknown_count):
              candidate = candidate.replace('x', item, 1)
          if luhn_validate(candidate):
              print(candidate)
docs: Having known values for a Luhn validated number, obtain the possible unknown numbers.
  
      Numbers that use the Luhn algorithm for validation are Credit Cards, IMEI,
      National Provider Identifier in the United States, Canadian Social
      Insurance Numbers, Israel ID Numbers and Greek Social Security Numbers (ΑΜΚΑ).
  
      The '-' characters are ignored.
  
      Define the missing numbers with the 'x' character.
  
      Reference: https://en.wikipedia.org/wiki/Luhn_algorithm
  
      Example:
  
      \b
      $ habu.crack.luhn 4509-xxxx-3160-6445