import sys


class LookingGlass:
    def __enter__(self):
        # 將原始的 sys.stdout.write 函數(shù)保存起來
        self.original_wirte = sys.stdout.write
        # 將 sys.stdout.write 函數(shù)替換為 reverse_write 方法
        sys.stdout.write = self.reverse_wirte
        # 返回一個字符串作為上下文管理器的上下文對象
        return 'QWERTYUIOP'

    def reverse_wirte(self, text):
        # 對傳入的文本進行反轉(zhuǎn)后輸出
        return self.original_wirte(text[::-1])

    def __exit__(self, exc_type, exc_val, exc_tb):  # 如果一切正常，那么Python 調(diào)?__exit__ ?法時傳?的參數(shù)是None, None, None
        # 在退出上下文管理器時，恢復(fù)原始的 sys.stdout.write 函數(shù)
        sys.stdout.write = self.original_wirte
        # 如果發(fā)生的異常是 ZeroDivisionError，輸出相應(yīng)提示信息
        if exc_type is ZeroDivisionError:
            print('Please DO NOT divide by zero!')
            return True  # 返回True，告訴解釋器異常已處理


if __name__ == '__main__':
    with LookingGlass() as what:
        # print(obj)實質(zhì)就是調(diào)用sys.stdout.write(obj+'\n')
        print("床前明月光")  # 光月明前床
        print("疑是地上霜")  # 霜上地是疑
        print(what)  # POIUYTREWQ
    print(what)  # QWERTYUIOP 處理上下文管理器，輸出的文本正常，不再翻轉(zhuǎn)

import sys
import contextlib


@contextlib.contextmanager
def looking_glass():
    original_text = sys.stdout.write

    def reverse_write(text):
        original_text(text[::-1])

    sys.stdout.write = reverse_write
    msg = ''
    # 這里處理異常是因為如果with塊有異常拋出，Python會將其捕獲，然后再looking_glass函數(shù)的yield表達式再次拋出
    # 但是那里又沒有處理錯誤的代碼，因此looking_glass函數(shù)將終止執(zhí)行，永遠無法恢復(fù)成原來的sys.stdout.write方法，導(dǎo)致系統(tǒng)處于無效狀態(tài)。
    try:
        yield 'QWERTYUIOP'
    except ZeroDivisionError:
        msg = 'Please DO NOT divide by zero!'
    finally:
        sys.stdout.write = original_text
        if msg:
            print(msg)


if __name__ == '__main__':
    with looking_glass() as what:
        print("床前明月光")  # 光月明前床
        print("疑是地上霜")  # 霜上地是疑
        print(what)  # POIUYTREWQ
    print(what)  # QWERTYUIOP

@looking_glass()
def varse():
    print("舉頭望明月低頭思故鄉(xiāng)")

if __name__ == '__main__':
    varse() # 鄉(xiāng)故思頭低月明望頭舉