如何从pyparsing转发对象中获取结果？

from pyparsing import Word, nums, Forward, Group, Suppress, ZeroOrMore

expression = Forward()

integer = Word(nums).setParseAction(lambda t: int(t[0]))
operand = integer | Group(Suppress('(') + expression + Suppress(')'))
operator = Word('+-*/', max=1)
expression << operand + ZeroOrMore(operator + operand)

input_str = "2 + (3 * 4)"
result = expression.parseString(input_str, parseAll=True)

print(result[0])  # 输出结果：2
print(result[1])  # 输出结果：'+'
print(result[2])  # 输出结果：[3, '*', 4]