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[Python-ideas] Conventions for function annotations

Nick Coghlan ncoghlan at gmail.com
Sun Dec 2 12:43:34 CET 2012 
On Sun, Dec 2, 2012 at 8:12 PM, Robert McGibbon <rmcgibbo at gmail.com> wrote:

> Nick,
>
> Thanks! You make a very convincing argument.
>
> Especially if this represents the collective recommendation of the python
> core development team on the proper conventions surrounding the use of
> function annotations, I would encourage you guys to perhaps make it more
> widely known (blogs, etc). As python 3.x adoption continues to move
> forward, this type of thing could become an issue if shmucks like me start
> using the annotation feature more widely.
>

Last time it came up, the collective opinion on python-dev was still to
leave PEP 8 officially neutral on the topic so that people could experiment
more freely with annotations and the community could help figure out what
worked well and what didn't. Admittedly this was long enough ago that I
don't remember the details, just the obvious consequence that PEP 8 remains
largely silent on the matter, aside from declaring that function
annotations are off-limits for standard library modules: "The Python
standard library will not use function annotations as that would result in
a premature commitment to a particular annotation style. Instead, the
annotations are left for users to discover and experiment with useful
annotation styles."

Obviously, I'm personally rather less open-minded on the topic of
*composition* in particular, as that's a feature I'm firmly convinced
should be left in the hands of ordinary decorator usage. I believe trying
to contort annotations to handle that cause is almost certain to result in
something less readable than the already possible decorator equivalent.

However, the flip-side of the argument is that if we assume my opinion is
correct and document it as an official recommendation in PEP 8, then many
people won't even *try* to come up with good approaches to composition for
function annotations. Maybe there *is* an elegant, natural solution out
there that's superior to using explicit calls to decorator factories for
the cases that involve composition. If PEP 8 declares "just use decorator
factories for cases involving composition, and always design your APIs with
a non-annotation based fallback for such cases", would we be inadvertently
shutting down at least some of the very experimentation we intended to
allow?

After all, while I don't think the composition proposal in this thread
reached the bar of being more readable than just composing decorator
factories to handle more complex cases, I *do* think it is quite a decent
attempt.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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