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lib2to3 fails on a trailing comma after **kwargs in a function signature #77245

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ambv opened this issue Mar 13, 2018 · 9 comments
Closed

lib2to3 fails on a trailing comma after **kwargs in a function signature #77245

ambv opened this issue Mar 13, 2018 · 9 comments
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@ambv
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3.7 (EOL) end of life 3.8 only security fixes type-bug An unexpected behavior, bug, or error

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@ambv
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ambv commented Mar 13, 2018

BPO 33064
Nosy @ned-deily, @ambv, @serhiy-storchaka
PRs
  • bpo-33064: lib2to3: support trailing comma after **kwargs #6096
  • bpo-33064: lib2to3: support trailing comma after **kwargs #6096
  • [3.7] bpo-33064: lib2to3: support trailing comma after *args and **kwargs (GH-6096) #6097
  • [3.6] bpo-33064: lib2to3: support trailing comma after *args and **kwargs (GH-6096) #6098
  • bpo-33064: lib2to3: Add more tests #6101
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    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/ambv'
closed_at = <Date 2018-03-13.22:19:55.107>
created_at = <Date 2018-03-13.02:50:30.090>
labels = ['3.8', 'type-bug', '3.7']
title = 'lib2to3 fails on a trailing comma after **kwargs in a function signature'
updated_at = <Date 2018-03-13.22:19:55.106>
user = 'https://github.com/ambv'

    bugs.python.org fields:

    activity = <Date 2018-03-13.22:19:55.106>
actor = 'lukasz.langa'
assignee = 'lukasz.langa'
closed = True
closed_date = <Date 2018-03-13.22:19:55.107>
closer = 'lukasz.langa'
components = []
creation = <Date 2018-03-13.02:50:30.090>
creator = 'lukasz.langa'
dependencies = []
files = []
hgrepos = []
issue_num = 33064
keywords = ['patch', 'patch']
message_count = 9.0
messages = ['313718', '313719', '313722', '313723', '313724', '313725', '313726', '313728', '313729']
nosy_count = 3.0
nosy_names = ['ned.deily', 'lukasz.langa', 'serhiy.storchaka']
pr_nums = ['6096', '6096', '6097', '6098', '6101']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33064'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']
    @ambv
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    ambv commented Mar 13, 2018

    Title says all. I have a patch.

    @ambv ambv added 3.7 (EOL) end of life 3.8 only security fixes labels Mar 13, 2018
    @ambv ambv self-assigned this Mar 13, 2018
    @ambv
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    ambv commented Mar 13, 2018

    Ned, I'd like this to make into 3.6.5 if at all possible.

    @ambv ambv added the type-bug An unexpected behavior, bug, or error label Mar 13, 2018
    @serhiy-storchaka
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    Does it support a trailing comma after *args or name=value?

    @serhiy-storchaka
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    I'm not sure that a trailing comma after **kwargs in a function signature should be allowed in Python grammar. Reasons for allowing it after other arguments don't work here since **kwargs is always a last item in a signature.

    But this ship perhaps is sailed.

    @ambv
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    ambv commented Mar 13, 2018

    New changeset b51f5de by Łukasz Langa in branch 'master':
    bpo-33064: lib2to3: support trailing comma after *args and **kwargs (bpo-6096)
    b51f5de

    @ambv
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    ambv commented Mar 13, 2018

    Yes, this ship has sailed with Python 3.6.

    I understand your logic and this is indeed why we didn't support this for a long time. However, people tend to grow muscle memory to add trailing commas and that was tripping them over for no real gain on our part. So this was added. The reason I found out about lib2to3 not following suit was that 3.6 users quickly started to put those trailing commas in and tools using lib2to3 were crashing on such files :) This proves it was worth it.

    @ambv
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    ambv commented Mar 13, 2018

    Oh, and in terms of *calling* functions, now we can specify multiple unpacks, like:

      >>> f(
  ...   **d,
  ...   **e,
  ... )

    so the extra comma for signatures simply makes it symmetrical in terms of appearance.

    @ambv
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    ambv commented Mar 13, 2018

    New changeset b4c8871 by Łukasz Langa (Miss Islington (bot)) in branch '3.7':
    bpo-33064: lib2to3: support trailing comma after *args and **kwargs (GH-6096) (bpo-6097)
    b4c8871

    @ambv
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    ambv commented Mar 13, 2018

    New changeset 6a526f6 by Łukasz Langa (Miss Islington (bot)) in branch '3.6':
    bpo-33064: lib2to3: support trailing comma after *args and **kwargs (GH-6096) (bpo-6098)
    6a526f6

    @ambv ambv closed this as completed Mar 13, 2018
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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