core.py 文件源码

def expr(self):
        """
        Process the expression, by returning a sympy expression
        """
        if DEBUG:
            print("> ArithmeticExpression ")

        ret = self.op[0].expr
        for operation, operand in zip(self.op[1::2], self.op[2::2]):

            if operation == '+':
                ret = Add(ret, operand.expr)
            else:
                a   = Mul(-1, operand.expr)
                ret = Add(ret, a)

        return ret