def _reverse_operator(self, op):
op = copy.copy(op)<EOL>op.reverse()<EOL>if not str(op) in self.MONGO_OPS:<EOL><INDENT>raise ValueError('<STR_LIT>'.format(op))<EOL><DEDENT>return op<EOL>
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