Solve to the reversed polish notation evaluator engine

reversed_polish_evaluator

def eval_expr(operand,a,b):
    if operand == '+':
        return a + b
    elif operand == '-':
        return a - b
    elif operand == '*':
        return a * b
    else:
        return a / b

def reversed_polish(expr):
    list = []
    operands = ['+','-','*','/']
    for elem in expr:
        if elem in operands:
            second = list.pop()
            first = list.pop()
            result = eval_expr(elem,first,second)
            list.append(result)
        else:
            list.append(elem)
    print(list)        
    return list[0]



test = [1,2,3,'+',2,'*','-']
assert reversed_polish(test) == -9 ,"Wrong"