計算四則運(yùn)算：

import ninth lesson_Tree

def build_parse_Tree(alist):
    alst = alist.split()
    # 創(chuàng)建一個節(jié)點(diǎn)棧
    astack = []
    res_Tree = BinaryTree('')
    astack.append(res_Tree)
    currentTree = res_Tree

    for i in alst:
        # 如果是'('，則創(chuàng)建左子節(jié)點(diǎn)，并把該父節(jié)點(diǎn)記錄入棧，再把指針指向左子節(jié)點(diǎn)
        if i == '(':
            currentTree.insertLeft('')
            astack.append(currentTree)
            currentTree = currentTree.getLeftChildren()
        # 如果是數(shù)字，則給節(jié)點(diǎn)賦值，并把父節(jié)點(diǎn)出棧，再把指針指向父節(jié)點(diǎn)
        elif i is not in ['+', '-', '*', '/']:
            currentTree.setVal(int(i))
            currentTree = astack.pop()
        # 如果是符號，則給節(jié)點(diǎn)賦值符號，并把該節(jié)點(diǎn)入棧，并創(chuàng)建右子節(jié)點(diǎn)，再把指針指向右子節(jié)點(diǎn)
        elif i in ['+', '-', '*', '/']:
            currentTree.setVal(i)
            currentTree.insertRight('')
            astack.append(currentTree)
            currentTree = currentTree.getRightChildren()
        # 如果是')'，則返回上一節(jié)點(diǎn)，即將棧壓出上一節(jié)點(diǎn)
        elif i == ')':
            currentTree = astack.pop()

        else:
            raise ValueError

    return res_Tree

# 遞歸調(diào)用，基本結(jié)束條件為節(jié)點(diǎn)為葉節(jié)點(diǎn)，返回葉節(jié)點(diǎn)的值進(jìn)行計算
def evaluate(res_Tree):
    opers = {'+': operator.add(), '-': operator.sub(), '*': operator.mul(), '/': operator.truediv()}

    left = res_Tree.getLeftChildren()
    right = res_Tree.getRightChildren()

    if left and right:
        fn = opers[res_Tree.getRootVal()]
        return fn(evaluate(left),evaluate(right))
    else:
        return res_Tree.getRootVal()