new_contents: from zope.component import getUtility
  from IOperation import IOperation
  from zope.interface.interfaces import ComponentLookupError
  
  import registrator
  
  
  def calc(expr):
      a, op, b = expr.split()
      return getUtility(IOperation, op)(eval(a), eval(b))
  
  
  assert calc('2 + 2') == 4
  assert calc('2 - 2') == 0
  assert calc('2 - 0.2') == 1.8
  
  try:
      assert calc('2 * 2') == 4
  except:
      pass
  else:
      raise RuntimeError("Should raise ComponentLookupError because there is no operation * utility")
  
subject: Create main.py