code: def to_gremlin(self):
          
          self.validate()
          return u'({predicate} ? {if_true} : {if_false})'.format(
              predicate=self.predicate.to_gremlin(),
              if_true=self.if_true.to_gremlin(),
              if_false=self.if_false.to_gremlin())
docs: Return a unicode object with the Gremlin representation of this expression.