我经常在其他Stack Overflow问题上看到关于如何不鼓励使用except: pass的评论。这为什么不好呢?有时我不在乎错误是什么,我只想继续写代码。
try:
something
except:
pass
为什么使用except: pass块不好?是什么让它变得糟糕?是我传递了一个错误还是我排除了任何错误?
我经常在其他Stack Overflow问题上看到关于如何不鼓励使用except: pass的评论。这为什么不好呢?有时我不在乎错误是什么,我只想继续写代码。
try:
something
except:
pass
为什么使用except: pass块不好?是什么让它变得糟糕?是我传递了一个错误还是我排除了任何错误?
当前回答
这里的主要问题是它忽略所有和任何错误:内存不足,CPU正在燃烧,用户想要停止,程序想要退出,Jabberwocky正在杀死用户。
这太过分了。在你的脑海中,你在想“我想忽略这个网络错误”。如果出现了意想不到的错误,那么您的代码将继续以完全不可预测的方式中断,没有人可以调试。
这就是为什么您应该限制自己只忽略一些错误,而让其余的错误过去。
其他回答
>>> import this
The Zen of Python, by Tim Peters Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. Flat is better than nested. Sparse is better than dense. Readability counts. Special cases aren't special enough to break the rules. Although practicality beats purity. Errors should never pass silently. Unless explicitly silenced. In the face of ambiguity, refuse the temptation to guess. There should be one-- and preferably only one --obvious way to do it. Although that way may not be obvious at first unless you're Dutch. Now is better than never. Although never is often better than right now. If the implementation is hard to explain, it's a bad idea. If the implementation is easy to explain, it may be a good idea. Namespaces are one honking great idea -- let's do more of those!
所以,这是我的观点。每当你发现一个错误,你应该做一些事情来处理它,即把它写在日志文件或其他东西。至少,它告诉您曾经有一个错误。
我正在构建一个将在数据中心运行的应用程序。它不应该生成任何错误或引发任何异常。我的数据中心有一个网络监控系统,其中包括一个SNMP trap接收器。
try:
main()
except as e:
log(str(e))
send_snmp_trap(str(e))
raise
但是这个加薪不会有任何效果因为它是和任何可能剩下的堆栈的底部。
顺便说一句,这不是万能的灵丹妙药。有一些例外情况是无法被发现的。SNMP不能保证传输。YMMV。
你至少应该使用except Exception:来避免捕获系统异常,如SystemExit或KeyboardInterrupt。这里是文档链接。
一般来说,您应该显式地定义想要捕获的异常,以避免捕获不想要的异常。您应该知道您忽略了哪些异常。
通常,您可以将任何错误/异常分为以下三类之一:
Fatal: Not your fault, you cannot prevent them, you cannot recover from them. You should certainly not ignore them and continue, and leave your program in an unknown state. Just let the error terminate your program, there is nothing you can do. Boneheaded: Your own fault, most likely due to an oversight, bug or programming error. You should fix the bug. Again, you should most certainly not ignore and continue. Exogenous: You can expect these errors in exceptional situations, such as file not found or connection terminated. You should explicitly handle these errors, and only these.
在除了:pass之外的所有情况下,pass只会让你的程序处于未知状态,在这种状态下它会造成更多的损害。
In my opinion errors have a reason to appear, that my sound stupid, but thats the way it is. Good programming only raises errors when you have to handle them. Also, as i read some time ago, "the pass-Statement is a Statement that Shows code will be inserted later", so if you want to have an empty except-statement feel free to do so, but for a good program there will be a part missing. because you dont handle the things you should have. Appearing exceptions give you the chance to correct input data or to change your data structure so these exceptions dont occur again (but in most cases (Network-exceptions, General input-exceptions) exceptions indicate that the next parts of the program wont execute well. For example a NetworkException can indicate a broken network-connection and the program cant send/recieve data in the next program steps.
但是只对一个执行块使用pass块是有效的,因为你仍然可以区分不同类型的异常,所以如果你把所有的异常块放在一个中,它就不是空的:
try:
#code here
except Error1:
#exception handle1
except Error2:
#exception handle2
#and so on
可以写成这样:
try:
#code here
except BaseException as e:
if isinstance(e, Error1):
#exception handle1
elif isinstance(e, Error2):
#exception handle2
...
else:
raise
因此,即使是多个带有pass语句的异常块也可能导致代码,其结构处理特殊类型的异常。