On 1/11/21 5:05 PM, Greg Ewing wrote:
On 12/01/21 6:22 am, Larry Hastings wrote:
* The language will set __annotations__ to a dict if the object has
annotations, or None if it has no annotations.
That sounds inconvenient -- it means that any code referencing
__annotations__ has to guard against the possibility of it being
None.
It was a balancing act. Using an 64-byte empty dict per object with no
defined annotations seems so wasteful. And anything short of an empty
dict, you'd have to guard against. Current code already has to guard
against "__annotations__ aren't set" anyway, so I figured the cost of
migrating to checking a different condition would be small. And None is
so cheap, and the guard is so easy:
if o.__annotations__:
If we're changing things, I'm wondering if the best thing would be
to introduce an annotations() function as the new best practice for
getting an object's annotations. It would know how to handle all
the type-specific pecularities, and could take care of things such
as manufacturing an empty dict if the object doesn't have any
annotations.
I guess I'm marginally against this, just because it seems like a
needless change. We don't need the flexibility of a function with
optional parameters and such, and with a data descriptor we can already
put code behind __annotations__ (as I have already done). Plus, the
function should probably cache its result--you wouldn't want code that
called it ten times to generate ten fresh dicts, would you?--and already
we're most of the way to what I proposed in PEP 649.
Cheers,
//arry/
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