On Wed, Feb 20, 2019 at 3:26 AM Grant Edwards <[email protected]> wrote:
>
> On 2019-02-19, Chris Angelico <[email protected]> wrote:
>
> > Oh, and not just bugs either. If the user hits Ctrl-C at just the
> > right moment, KeyboardInterrupt will be raised. You'll swallow that
> > exception silently, preventing the user-requested halt, and going and
> > doing the wrong thing. Don't use a bare except clause even if your
> > code is 100% perfect every time. (And anyone who thinks their code is
> > perfect hasn't tested it.)
>
> IMO, you're allowed to use a bare except clause to do cleanup or
> logging as long as the execption handler ends with the line
>
> raise
>
Yeah, I was clearer about that in the first email, to which that was a
followup, but I'll give two examples of valid bare-except constructs:
1) Handle-and-raise
try:
weird stuff
except:
show failure state
raise
2) Log-and-continue
while True:
try:
thing = get_next_thing()
except NoMoreThings, KeyboardInterrupt:
break
try:
response = some_handler(thing)
except:
response = 500
log_error()
try:
thing.respond(response)
except OSError:
pass
The implication of the second one is that (a) bugs in some_handler()
shouldn't break the whole program, and (b) attempting to halt
some_handler() with Ctrl-C shouldn't halt the whole program. It
creates a boundary.
But you should ALWAYS either reraise or log the exception. ALWAYS.
Otherwise, be specific about what you're swallowing.
ChrisA
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