evaluate and return the expression of the op on a and b

        Parameters
        ----------

        op :    the actual operand
        op_str: the string version of the op
        a :     left operand
        b :     right operand
        use_numexpr : whether to try to use numexpr (default True)

def evaluate(op, op_str, a, b, use_numexpr=True,
             **eval_kwargs):
    """ evaluate and return the expression of the op on a and b

        Parameters
        ----------

        op :    the actual operand
        op_str: the string version of the op
        a :     left operand
        b :     right operand
        use_numexpr : whether to try to use numexpr (default True)
        """

    use_numexpr = use_numexpr and _bool_arith_check(op_str, a, b)
    if use_numexpr:
        return _evaluate(op, op_str, a, b, **eval_kwargs)
    return _evaluate_standard(op, op_str, a, b)