二叉树的应用：表达树的代码实现（python语言）

灰太狼 2022-05-24 12:28 160阅读 0赞

![这里写图片描述][70]

def make_sum(a, b):  # 加
        return ['+', a, b]
    
    
    def make_prod(a, b):  # 乘
        return ['*', a, b]
    
    
    def make_diff(a, b):  # 减
        return ['-', a, b]
    
    
    def make_div(a, b):  # 除
        return ['/', a, b]
    
    
    def is_basic_exp(a):  # 判别是否为基本表达式
        return not isinstance(a, list)
    
    
    def eval_exp(e):
        if is_basic_exp(e):
            return e
        op, a, b = e[0], eval_exp(e[1]), eval_exp(e[2])
        if op == '+':
            return eval_sum(a, b)
        elif op == '-':
            return eval_diff(a, b)
        elif op == '*':
            return eval_prod(a, b)
        elif op == '/':
            return eval_div(a, b)
        else:
            raise ValueError("Unkown opterator:", op)
    
    
    def eval_sum(a, b):  # 加
        if isinstance(a, Number) and isinstance(b, Number):  # 如果a是一个数字并且b也是一个数字
            return a+b
        if isinstance(a, Number) and a == 0:
            return b
        if isinstance(b, Number) and b == 0:
            return a
        return make_sum(a, b)
    
    
    def eval_div(a, b):  # 除
        if isinstance(a, Number) and isinstance(b, Number):
            return a / b
        if isinstance(a, Number) and a == 0:
            return 0
        if isinstance(b, Number) and b == 1:
            return a
        if isinstance(b, Number) and b ==0:
            raise ZeroDivisionError
        return make_div(a, b)
    
    
    def eval_prod(a, b):  # 乘
        if isinstance(a, Number) and isinstance(b, Number):
            return a * b
        if isinstance(a, Number) and a == 0:
            return 0
        if isinstance(b, Number) and b == 0:
            return 0
        if isinstance(a, Number) and a == 1:
            return b
        if isinstance(b, Number) and b == 1:
            return a
        return make_prod(a, b)
    
    
    def eval_diff(a, b):  # 减
        if isinstance(a, Number) and isinstance(b, Number):
            return a - b
        if isinstance(a, Number) and a == 0:
            return -b
        if isinstance(b, Number) and b == 0:
            return a
        return make_diff(a, b)

[70]: /images/20220524/72d58674182e4841abf2bbd30066b312.png