Why assert is not a function?

[Chris Angelico]

On Sat, Mar 13, 2021 at 12:11 AM Richard Damon <Richard at damon-family.org> wrote:
>
> On 3/12/21 12:31 AM, Chris Angelico wrote:
> > On Fri, Mar 12, 2021 at 3:53 PM Cameron Simpson <cs at cskk.id.au> wrote:
> >> 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.
> > Something like that, yeah. An assertion failure represents a bug *in
> > this code*, something that shouldn't ever happen. If it's possible to
> > trigger the failure with some other piece of code (calling something
> > with bad arguments, or whatever), then assert is the wrong tool for
> > the job. Similarly, if you find yourself catching AssertionError
> > anywhere outside of unit testing, something is horribly wrong
> > somewhere :)
> >
> > ChrisA
>
> Chris, I would disagree with that statement. An assert says that there
> is something wrong with THE code, not THIS code. It is perfectly
> reasonable, and good defensive programming, to assert on the
> per-conditions to the procedure at its beginning.
>
> Now, it may be true that a 'friendlier' procedure may be defined to
> check some of these and return an error, but that then locks that
> behavior into the API, so the cost of the check becomes an absolute
> requirement.
>

It's perfectly reasonable to put "if condition: raise Blah", but is it
really reasonable to use the assert statement, which (a) might not be
run, and (b) raises a very generic exception? Make assertions about
your own code, not other people's.

ChrisA