new_contents: import itertools
  
  # http://www.macdevcenter.com/pub/a/python/excerpt/pythonckbk_chap1/index1.html?page=2
  def infinite_eratosthenes():
      composites = set()
      for i in itertools.count(2):
          if i not in composites:
              yield i
              composites.add(i * i)
  
subject: Create primes.py