异常的构成:
1.异常类2.异常值3.追踪信息(解释器捕捉到的)
def __exit__(self, exc_type, exc_val, exc_tb): print('do exit') print('exc_type异常的类:',exc_type) print('exc_val异常的内容',exc_val) print('exc_tb异常的追踪:',exc_tb)