On 1/11/21 6:34 PM, Paul Bryan wrote:
On Mon, 2021-01-11 at 17:56 -0800, Larry Hastings wrote:
On 1/11/21 5:02 PM, Paul Bryan wrote:
I'm probably naive, but is there a reason that one could not just
store a callable in __annotations__, and use the descriptor to
resolve it to a dictionary and store it when it is accessed? It
would be one less dunder in the Python data model.
That would work, but I think the API is a bit of a code smell.
__annotations__ would no longer be stable:
a.__annotations__ = o
assert a.__annotations__ == o
Would that assert fail? It depends on what type(o) is, which is
surprising.
Equally surprising?:
a.__co_annotations__ = o
a.__annotations__
assert a.__co_annotations__ == o
I've ruminated about this a bit over the past few days, and I finally
realized exactly why, yes, I think behavior is more surprising. It's
because __annotations__ is now 12 years old (!), and never in that
entire time has it silently changed its value. It's always been
completely stable, and we have twelve years' worth of installed base
that may rely on that assumption. In comparison, __co_annotations__ is
a new attribute. While it's also surprising that __co_annotations__ can
be automatically unset, at least this would be a documented part of its
behavior from day 1.
Relatedly, __co_annotations__ is behaving somewhat like a cached value,
in that cached values get deleted when they're out-of-date. (An
observation that may provide some guidance if we decide to rename
__co_annotations__.) This idiom may be familiar to the user--unlike
your proposed semantics, which I don't recall ever seeing used in an API.
I admit it's only a small difference between what you proposed and what
I propose, but in the end I definitely prefer my approach.
Cheers,
//arry/
_______________________________________________
Python-Dev mailing list -- python-dev@python.org
To unsubscribe send an email to python-dev-le...@python.org
https://mail.python.org/mailman3/lists/python-dev.python.org/
Message archived at
https://mail.python.org/archives/list/python-dev@python.org/message/HVIVCQ6AONKRZYWNY4VYHAOWT3WTEJAF/
Code of Conduct: http://python.org/psf/codeofconduct/
