exception problem

Andrew Berg bahamutzero8825 at gmail.com
Mon Jun 25 08:23:52 CEST 2012


On 6/25/2012 12:27 AM, Charles Hixson wrote:
> The documentation section covering the except statement could stand to 
> be a *LOT* clearer.   I read the sections on the except statement and 
> exception handlers several times and couldn't figure out was the "as" 
> argument of the except statement was for.
I agree that the tutorial doesn't explain the use of "as" very well, but
it does cover that a bare except is not normally good to use:
"The last except clause may omit the exception name(s), to serve as a
wildcard. Use this with extreme caution, since it is easy to mask a real
programming error in this way!"

> I still don't really know what 
> "as" means, except that if you use it, and you print out the "target", 
> you'll get some kind of informative message.
"as" lets you refer to the exception object that was caught. I find this
useful mainly for exceptions that have attributes (most built-in
exceptions don't, but many user-defined exceptions do). A full traceback
is much more useful for debugging than what a simple print(exc) will give.
There are a few different ways to get traceback information without
letting the exception simply propagate and terminate the program. You
can get some simple information from sys.exc_info() (and you can feed
the traceback object to a function in the traceback module), or you can
log it with the logging.exception() function or the exception() method
of a Logger from the same module. I recommend using logging. However,
it's generally best to just let any unexpected exceptions propagate
unless the program absolutely must continue, especially when debugging.
-- 
CPython 3.3.0a4 | Windows NT 6.1.7601.17803


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