M.-A. Lemburg wrote:
> Hi Ram,
>
> I think you are confusing the exception type with the exception
> reason. By adding 100 more exception types, you don't make things
> easier, but instead you complicate things, since we'd all have
> to memorize those 100 exception types.
>
> That said, enhancing the error reasons texts is certainly something
> that would help everyone.
>
> Adding more exception types to the stack makes sense when there's
> a dedicated need to catch only specific sub types, but even there
> it's already possible to add this extra information to the exception
> objects as e.g. .errno or similar attribute.
There is prior art, though, specifically for errno:
$ python2 -c 'open("not-there")'
Traceback (most recent call last):
File "<string>", line 1, in <module>
IOError: [Errno 2] No such file or directory: 'not-there'
$ python3 -c 'open("not-there")'
Traceback (most recent call last):
File "<string>", line 1, in <module>
FileNotFoundError: [Errno 2] No such file or directory: 'not-there'
I very much prefer the specific exception because most of the time I only
want to handle the common problems. Instead of
try:
open file
except OSError as err:
if err.errno == what was file-not-found? ah ENOENT:
# deal with it
elif err.errno == what was is-a-directory? ah EISDIR:
# deal with it
else:
# give up
raise
I can now write
try:
open file
except FileNotFoundError:
# deal with it
except IsADirectoryError:
# deal with it
which (a) looks better to me and (b) is easier to remember. It's a bit like
Guido's advice to use distinct functions instead of flags.
I am sure that I would quickly adopt more specific exceptions in other areas
(most notably HTTPError). I don't think they all need to become built-ins.
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