functools.WRAPPER_ASSIGNMENTS should include __annotations__

[terrence]

BPO	8814
Nosy	@rhettinger, @pitrou, @merwok, @david-caro
PRs	gh-85403: Make wraps retain type annotations #21392
Files	functools-wrapper-assign-annotations.diff: Patch to add annotations to WRAPPER_ASSIGNMENTS functools-wrapper-assign-annotations.diff: Improved patch with documentation fixed to match. functools-wrapper-assign-annotations.diff: Improved patch with documentation and tests

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/rhettinger'
closed_at = <Date 2010-08-08.00:57:27.438>
created_at = <Date 2010-05-24.21:20:57.698>
labels = ['type-bug', 'library']
title = 'functools.WRAPPER_ASSIGNMENTS should include __annotations__'
updated_at = <Date 2020-07-08.09:16:01.461>
user = 'https://bugs.python.org/terrence'

bugs.python.org fields:

activity = <Date 2020-07-08.09:16:01.461>
actor = 'David Caro'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2010-08-08.00:57:27.438>
closer = 'rhettinger'
components = ['Library (Lib)']
creation = <Date 2010-05-24.21:20:57.698>
creator = 'terrence'
dependencies = []
files = ['17453', '17454', '17694']
hgrepos = []
issue_num = 8814
keywords = ['patch']
message_count = 13.0
messages = ['106394', '106396', '106402', '107759', '107974', '112851', '112852', '112856', '112858', '112860', '112874', '112903', '113220']
nosy_count = 5.0
nosy_names = ['rhettinger', 'pitrou', 'eric.araujo', 'terrence', 'David Caro']
pr_nums = ['21392']
priority = 'normal'
resolution = 'fixed'
stage = 'test needed'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue8814'
versions = ['Python 3.1', 'Python 3.2']

[terrence]

__annotations__ should be included in the set of attributes copied by default to a wrapped method.

An example of the problem:
>>> from functools import wraps
>>> def mydecorator(fn):
...     @wraps(fn)
...     def inner(*args, **kwargs):
...         return fn(*args, **kwargs)
...     return inner
...
>>> @mydecorator
... def foo(a:int, b:str):
...     pass
... 
>>> foo.__annotations__
{}

With the included fix:
>>> foo.__annotations__
{'a': <class 'int'>, 'b': <class 'str'>}

[merwok]

The patch is fine. Can you check if some doc has to be updated to mention that? (files under Doc and docstrings in functools.py).

Removing 3.1 since this is a new feature, and 3.3 since 3.2 is not frozen.

[terrence]

Thank you for looking it over! The updated patch adds __annotations__ to the documentation where the value of WRAPPER_ASSIGNMENTS is given. I think it would be nice if the documentation showed WRAPPER_ASSIGNMENTS and WRAPPER_UPDATES in their own section, but that would probably merit a separate issue to fix, if it is even worth bothering with.

[merwok]

Patch looks good to me. Could you add some tests to Lib/test/test_functools.py to check that annotations are really copied?

(3.2 is not frozen, adjusting versions)

[terrence]

Alright, I've added several tests. I also modified update_wrapper to not copy missing attributes (like __annotations__ on builtin methods) -- see bpo-1576241.

(I also finally see what you mean with removing 3.3 from the versions list. Sorry I didn't grok that before.)

[terrence]

Is there still a chance to get this fix in 3.2?

[pitrou]

The patch is now committed in py3k (r83731). Thanks for your contribution!

[rhettinger]

This should probably be backported to 3.1

[pitrou]

This should probably be backported to 3.1

Well, I think this is technically a new feature. If someone wants to
backport it, then fine, but I don't think there's much point in doing
so.

[rhettinger]

Okay, I'll do it.

The intention of wrapper assignments was to wrap all of the standard attributes, so the omission of __annotations__ is a bug.

[terrence]

Awesome! I greatly appreciate the 3.1 backport, as that's what I'm going to be using for the foreseeable future.

[merwok]

Thanks for sticking with this Terrence, it fell off my radar. Thanks Antoine for the commit.

[rhettinger]

Backported to Py3.1 in r83807