code: def _reverse_operator(self, op):
          
          op = copy.copy(op)
          op.reverse()
          # check that we can map it
          if not str(op) in self.MONGO_OPS:
              raise ValueError('unknown operator: {}'.format(op))
          return op
docs: Reverse the operation e.g. since the conditions
          you provide are assertions of how things should be,
          e.g. asserting (a > b) leads to a search for (a <= b)
  
          :param op: Operator for any field/value
          :type op: ConstraintOperator