bpo-38605: Revert making 'from __future__ import annotations' the default

[pablogsal]

https://bugs.python.org/issue38605

[gousaiyang]

Hi @pablogsal, you may also want to revert my previous PR #25236 for this.

[vstinner]

Could you give a little bit context to explain the revert? I guess that it's related to the many threads on python-dev about it?

[pablogsal]

Is explained in the NEWs entry. I plan to explain it also on the final commit :)

[vstinner]

Oh ok, thanks. Copy of the NEWS entry:

Revert making 'from future import annotations' the default. This follows
the Steering Council decision to postpone PEP 563 changes to at least Python
3.11. See the original email for more information regarding the decision:
https://mail.python.org/archives/list/python-dev@python.org/thread/CLVXXPQ2T2LQ5MP2Y53VVQFCXYWQJHKZ/.
Patch by Pablo Galindo.

[isidentical]

@pablogsal also please bump the magic number (cached pycs might cause some issues) (it wasn't done in the initial PR, but rather get picked up on #22630)

[pablogsal]

@pablogsal also please bump the magic number (cached pycs might cause some issues) (it wasn't done in the initial PR, but rather get picked up on #22630)

We should be able to go back a version, I think. Cached pycs for alpha versions should not take lots of consideration

[pablogsal]

We should be able to go back a version, I think. Cached pycs for alpha versions should not take lots of consideration

Crap, there has been quite a lot of changes since then. Ok, bumping it is!

[pablogsal]

@pablogsal also please bump the magic number (cached pycs might cause some issues) (it wasn't done in the initial PR, but rather get picked up on #22630)

Done in ef38777a1f

[vstinner]

Oops sorry, I wanted to remove my comment rather posting it, but I closed the PR instead... I reopened the PR.

[gousaiyang]

We can also update the doc of __future__ module and Lib/__future__.py to mention that annotations feature is postponed to be "mandatory in 3.11".

[pablogsal]

cpython/Python/ceval.c

Lines 4363 to 4366 in d35eef3

	if (oparg & 0x04) {
	assert(PyTuple_CheckExact(TOP()));
	func->func_annotations = POP();
	}

This line should be changed to assert(PyTuple_CheckExact(TOP()) || PyDict_CheckExact(TOP()));.
I don't know why this pull request passes the test...

Are you taking #23316 into consideration?

[methane]

Are you taking #23316 into consideration?

Yes. And I know understand why this assrtion passes.

def add(a: int, b: int) -> int:
    return a + b

  3           0 LOAD_CONST               0 ('a')
              2 LOAD_NAME                0 (int)
              4 LOAD_CONST               1 ('b')
              6 LOAD_NAME                0 (int)
              8 LOAD_CONST               2 ('return')
             10 LOAD_NAME                0 (int)
             12 BUILD_TUPLE              6
             14 LOAD_CONST               3 (<code object add at 0x7f30fc37b050, file "a.py", line 3>)
             16 LOAD_CONST               4 ('add')
             18 MAKE_FUNCTION            4 (annotations)
             20 STORE_NAME               1 (add)

Annotation is tuple even when PEP 563 is disabled. That's nice.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @pablogsal for commit 51a6f52234cf416f33a8f8ce625502dedd2bf0fd 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[pablogsal]

I still would like if someone can formally approve the PR :)

[methane]

I have not reviewed tests yet. In other parts, LGTM.

[vstinner]

LGTM but please address first the comment in Lib/test/test_dataclasses.py (I concur that it looks a revert of a bugfix, so it reintroduces a typo).

I suggest to first revert the change, and then write a second PR to announce that annotations are going to change again (in Python 3.11 or later).

[pablogsal]

I suggest to first revert the change, and then write a second PR to announce that annotations are going to change again (in Python 3.11 or later).

@vstinner What do you mean when you say "announce"? Announce where? In the What's new? A news entry? python-dev?

I suggest to first revert the change

Notice that this was certainly not a clean revert

[vstinner]

@vstinner What do you mean when you say "announce"? Announce where? In the What's new? A news entry? python-dev?

Add a What's New in Python 3.10 entry to explain that the behavior changed but was then revert, and that it will change again in a future Python version.

Something like this announcement of future collections incompatible changes (collections.Mapping alias):
https://docs.python.org/dev/whatsnew/3.9.html#you-should-check-for-deprecationwarning-in-your-code

This announce was correct: the aliases were removed again in Python 3.10.

python-dev?

Any additional communication would be good, but the minimum would be a note in the What's New in Python 3.10.

[vstinner]

LGTM.