old_contents: """
  Module to test for primes.
  """
  
  
  def is_prime(number):
      "Test if number is prime."
  
      if number == 1:
          return False
  
      for factor in range(2, number):
          if number % factor == 0:
              return False
      return True
  
new_contents: """
  Module to test for primes.
  """
  
  
  def is_prime(number):
      "Test if number is prime."
  
      if number <= 0:
          raise TypeError("is_prime expects natural number argument")
  
      if number == 1:
          return False
  
      for factor in range(2, number):
          if number % factor == 0:
              return False
      return True
  
subject: fix Primes.is_prime to raise TypeError for numbers <= 0