python异常

try:
#引发异常的代码
excep (异常类1，异常类2，...,异常类n) as 异常值：
#捕作异常后，执行此语句块，没捕作到向上传播，直到主程序终止并显示跟踪消息
else:
#try下语句块没有异常错误，执行此语句块
finally:
#不管有没有引发异常，ecpect有没有捕作到异常，都执行此语句块

不能有try....else...组合，其它都行
except Exception : #这表示能捕捉到Exception及其派生子类的异常
except:   #这表示能捕捉到所有异常

raise

>>raise Exception
Traceback (most recent call last):

  File "", line 1, in 
    raise Exception

Exception
###只抛出了异常类

>>raise Exception('异常值')
Traceback (most recent call last):

  File "", line 1, in 
    raise Exception('异常值')

Exception: 异常值
#有异常类，也有值

def faulty():
    raise Exception('Something is wrong')
        
def ignore_exception():
    faulty()
    
def handle_exception():
    try:
        faulty()
    except:
        print('Exception handled')

>>ignore_exception()
Traceback (most recent call last):

  File "", line 14, in 
    ignore_exception()

  File "", line 5, in ignore_exception
    faulty()

  File "", line 2, in faulty
    raise Exception('Something is wrong')

Exception: Something is wrong

>>handle_exception()
Exception handled

#faulty中引发的异常依次从faulty和ignore_exception向外传播，最终显示一条跟踪消息。
#调用handle_exception时,异常最终传播到handle_exception，并被这里的try/except语句处理

try:
    1/0
except ZeroDivisionError:
    raise

Traceback (most recent call last):

  File "", line 2, in 
    1/0

ZeroDivisionError: division by zero    

#捕获异常后，如果要继续引发它（即继续向上传播），可调用raise且不提供任何参数

try:
    1/0
except ZeroDivisionError:
    raise ValueError

Traceback (most recent call last):

  File "", line 5, in 
    raise ValueError

ValueError

assert 表达式 [, 参数]

age = 10
>>assert 0>assert 0>assert 0", line 1, in 
    assert 0>assert 0", line 1, in 
    assert 0