new_contents: from zope.interface import Interface, implements
  from zope.component import getUtility
  from zope.component import adapts
  
  
  class IOperation(Interface):
      def __call__(a, b):
          """Performs operation on two operands"""
  
  
  class Plus(object):
      implements(IOperation)
  
      def __call__(self, a, b):
          return a + b
  
  
  # plus = Plus() # not needed if you use factory instead of component in configure.zcml
  
  
  class Minus(object):
      implements(IOperation)
  
      def __call__(self, a, b):
          return a - b
  
  
  # minus = Minus() # not needed if you use factory instead of component in configure.zcml
  
  
  
  class IScalaOperation(Interface):
      def apply(a, b):
          ''' performs operation on two operands '''
  
  
  class Division(object):
      implements(IScalaOperation)
  
      def apply(self, x, y):
          return x / y
  
  
  class ScalaOperationAdapter(object):
      implements(IOperation)
      adapts(IScalaOperation)
  
      def __init__(self, scala_op):
          self.scala_op = scala_op
  
      def __call__(self, a, b):
          return self.scala_op.apply(a, b)
  
subject: Create calc.py