Python 异常

try的工作原理是，开始一个try语句后，Python就在当前程序的上下文中做标记，当出现异常时就可以回到做标记的地方。首先执行try子句，接下来发生什么依赖于执行时是否出现异常。


 如果try后的语句执行时发生异常，程序就跳回try并执行except子句。异常处理完毕后，控制流就可以通过整个try语句了（除非在处理异常时又引发新异常）。

<pre class="brush:python;toolbar:false">class TestError(Exception):
 def __init__(self, errcode, errmsg):
 self.errcode = errcode
 self.errmsg = errmsg

def __str__(self):
        return f'errcode:{self.errcode},errmsg:{self.errmsg}'

def ex(execption_type):
    try:
        if execption_type == 'raise':
            raise Exception('raise threw Exception')
        elif execption_type == 'assert':
            assert 0 > 0, 'assert threw Exception'
        elif execption_type == 'test':
            raise TestError(0x0012, 'error message undefinde')
    except AssertionError as e:
        print(e)
    except TestError as e:
        print(e)
    except Exception as e:
        print(e)  ##e.__str__()
    else:
        print('if no errors ,i do')
    finally:
        print('i always do')

ex('raise')
# raise threw Exception
# i always do

ex('assert')
# assert threw Exception
# i always do

ex('test')
#errcode:18,errmsg:error message undefinde
#i always do

ex('ok')
# if no errors ,i do
# i always do</pre>