On 12Mar2021 12:53, DL Neil <pythonl...@danceswithmice.info> wrote:
>On 12/03/2021 11.27, Chris Angelico wrote:
>> On Fri, Mar 12, 2021 at 9:10 AM Ethan Furman <et...@stoneleaf.us> wrote:
>>> On 3/11/21 1:45 PM, dn via Python-list wrote:
>>>> Is assert so much faster/cheaper than try...except...raise?
>>>
>>> Infinitely faster when they are not there. ;-)
[...]
>> There are many hybrids available too though. For instance:
>>
>> if __debug__ or args.verify:
>> def verify(thing):
>> ...
>> raise Whatever
>> else:
>> def verify(thing): pass
>>
>> Yes, you pay the price of a function call even if you're not verifying
>> the full structural integrity. But that's a lot cheaper than the full
>> check.
>>
>> Advantage here is that you can use -O to suppress, or you can control
>> it with an arg, or whatever.
>>
>> If you're doing the same check in lots of places, and it's costly,
>> assertions aren't really a great fit.
>
>Perhaps I misunderstood (and haven't gone back to check - mea culpa),
>but the impression-gained was that -O many not be used, even "in
>production", for some reason?
News to me. Perhaps that was someone's scenario.
To me, asserts have 2 primary features: (a) they're easy to write (and
read) versus "if some_test: raise SomeException("blah blah...")" and (b)
they are outright _absent_ from the code when run with -O.
_Provided_ the code called from the assert has no side effects, dropping
the asserts should always make for identical -O behaviour vs no -O.
Chris' example above walks the middle ground providing something richer
that a plain assert while still (almost) vanishing with -O (and no
args.verify mode switch).
>Perhaps because I've not come from a language where assert played any/a
>major rôle, but am still hoping for some discussion/understanding as to
>why/when assert might be better than try...except in every/particular
>situations...
I find assert visually low impact. Try/except is quite wordy and brings
more indentation.
One has to keep in mind the use case.
For me, try/except is for when something might reasonably "go wrong" in
normal use, even niche normal use. Whereas assert is for things which
should _never_ occur. Roughly, again for me, try/except if for catching
misuse and assert is for catching misdesign/misimplementation.
Cheers,
Cameron Simpson <c...@cskk.id.au>
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