new_contents: import argparse
  import random
  
  
  def main():
      parser = argparse.ArgumentParser(description="Tesco's deal mistake, implemented in Python.")
      parser.add_argument('barcode', type=str, help='Original barcode')
      parser.add_argument('price', type=str, help='Desired price in pence')
      parser.add_argument('mystery', type=str, nargs="?", default=False, help='Manually set the mystery arg')
      args = parser.parse_args()
  
      print calculate_barcode(args.barcode, args.price, args.mystery)
  
  
  def calculate_barcode(barcode, price, mystery=False):
      new = "971{barcode}{mystery}{price}0".format(
          barcode=barcode,
          mystery=mystery or str(random.randint(0, 9)),
          price=price.zfill(5))
  
      evens_checksum = sum(int(char) for i, char in enumerate(new) if (i + 1) % 2 == 0)
      odds_checksum = sum(int(char) for i, char in enumerate(new) if (i + 1) % 2 != 0) * 3
      checksum = 10 - ((evens_checksum + odds_checksum) % 10)
  
      return new + str(checksum)
  
  
  if "__main__" == __name__:
      main()
  
subject: Add tescohdear python file