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Title: singledispatch support for type annotations
Type: enhancement Stage: resolved
Components: Library (Lib) Versions: Python 3.7
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: lukasz.langa Nosy List: cheryl.sabella, gvanrossum, levkivskyi, lukasz.langa, rhettinger, yselivanov
Priority: normal Keywords: patch

Created on 2017-12-05 21:24 by lukasz.langa, last changed 2022-04-11 14:58 by admin. This issue is now closed.

Pull Requests
URL Status Linked Edit
PR 4733 merged lukasz.langa, 2017-12-05 21:26
PR 6114 xiang.zhang, 2018-03-14 22:24
Messages (8)
msg307686 - (view) Author: Łukasz Langa (lukasz.langa) * (Python committer) Date: 2017-12-05 21:24
With the patch attached to this issue, @singledispatch gains support for passing the type in @register via annotations.

This looks more natural and enables more thorough type checking without repeating yourself:

def generic(arg): ...

def _(arg: str): ...

def _(arg: int): ...

The previous API is still available for backwards compatibility, as well as stacking, and use with classes (sic, I was surprised to learn it's used that way, too).

The patch should be uncontroversial, maybe except for the fact that it's importing the `typing` module if annotations are used. This is necessary because of forward references, usage of None as a type, and so on. More importantly, with PEP 563 it's mandatory.
msg307690 - (view) Author: Łukasz Langa (lukasz.langa) * (Python committer) Date: 2017-12-05 21:40
Guido, I know that you have a lot on your plate right now. Adding you because of PEP 443 and PEP 484.
msg307691 - (view) Author: Ivan Levkivskyi (levkivskyi) * (Python committer) Date: 2017-12-05 21:42
Idea looks interesting (like a basic runtime @overload). My expectation is that some changes are necessary in mypy for this to work properly.

Another (minor) problem is that this creates a circular dependency functools <-> typing.
msg307692 - (view) Author: Ivan Levkivskyi (levkivskyi) * (Python committer) Date: 2017-12-05 21:43
Oops something wrong happened.
msg307693 - (view) Author: Łukasz Langa (lukasz.langa) * (Python committer) Date: 2017-12-05 21:58
> this creates a circular dependency functools <-> typing

Well, it doesn't since I explicitly import typing inside singledispatch. By the time this import happens, functools is fully imported. This would only be a problem if functools itself tried to use singledispatch with annotations. Not impossible but super unlikely.
msg308075 - (view) Author: Łukasz Langa (lukasz.langa) * (Python committer) Date: 2017-12-11 21:56
New changeset e56975351bc2c574c728f738e88effba7116279f by Łukasz Langa in branch 'master':
bpo-32227: functools.singledispatch supports registering via type annotations (#4733)
msg311565 - (view) Author: Cheryl Sabella (cheryl.sabella) * (Python committer) Date: 2018-02-03 17:35

I believe this could be closed as resolved?  Do you think it should be added to the What's New? page for 3.7?
msg311599 - (view) Author: Ivan Levkivskyi (levkivskyi) * (Python committer) Date: 2018-02-04 14:13
> Do you think it should be added to the What's New? page for 3.7?

I leave this up to Łukasz.
Date User Action Args
2022-04-11 14:58:55adminsetgithub: 76408
2018-03-14 23:34:12lukasz.langasetstatus: open -> closed
resolution: fixed
stage: patch review -> resolved
2018-03-14 22:24:41xiang.zhangsetstage: patch review
pull_requests: + pull_request5882
2018-03-14 22:23:48lukasz.langalinkissue27984 superseder
2018-02-04 14:13:49levkivskyisetmessages: + msg311599
2018-02-03 17:35:16cheryl.sabellasetnosy: + cheryl.sabella
messages: + msg311565
2017-12-11 21:56:33lukasz.langasetmessages: + msg308075
2017-12-05 21:58:51lukasz.langasetmessages: + msg307693
2017-12-05 21:43:57levkivskyisetnosy: + gvanrossum

messages: + msg307692
stage: patch review -> (no value)
2017-12-05 21:42:42levkivskyisetnosy: + levkivskyi, - gvanrossum
messages: + msg307691
stage: patch review
2017-12-05 21:40:04lukasz.langasetnosy: + gvanrossum

messages: + msg307690
stage: patch review -> (no value)
2017-12-05 21:26:44lukasz.langasetkeywords: + patch
stage: patch review
pull_requests: + pull_request4636
2017-12-05 21:24:12lukasz.langacreate