On 11/29/21 2:56 PM, Barry Warsaw wrote:
PEP 563 and 649 have visible effects that even within that domain can have important side effects. For example, PEP 563’s loss of local scope, which even “de-stringify-ing” can’t recover. This is what we need help with.
Well, sure. If PEP 563 and 649 didn't have visible effects, there'd be no point in doing them. That said, I suggest 649 does a lovely job of avoiding /undesirable/ side-effects.
Sure, 649 has observable side effects. For example, you can detect whether or not 649 is active by rebinding a name after it's used in an annotation but before examining that annotation at runtime. This seems harmless--unlikely to happen in production code, and easily remedied if someone did trip over it.
A more credible side effect: if you use an undefined name in an annotation, you won't notice at compile-time. Now, this is actually 649's major feature! But there are also scenarios where this feature could cover up a bug, like if you misspell a name--you won't notice until you examine the annotation at runtime (or, more likely, until you run your static analyzer). 563 has this same behavior--and it wasn't enough to prevent 563 being accepted. So I assume this wouldn't be enough to prevent accepting 649 either.
649 has effects on memory usage and performance, but honestly I'm not worried about these. I don't think the memory usage and performance of the prototype were particularly bad. Anyway, as I've said many times: we should figure out the semantics we want first, and then we can worry about optimization. The Python core dev community has no end of smart people who love optimizing things--I'm sure if 649 was accepted and merged, the optimizations would start rolling in.
Then of course there are also things 649 simply doesn't do, e.g. resolve the "if TYPE_CHECKING" situation. But it's not appropriate to call that a "side effect" per se.
And that's my list. If anybody knows of other visible side effects from 649, naturally you should contact the SC. And/or me, if you think we could change 649 to mitigate it without losing its major features.
Happy holidays, //arry/
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