dataclasses.InitVar breaks with typing.Optional

[samuelcolvin]

BPO	38431
Nosy	@ericvsmith, @serhiy-storchaka, @ilevkivskyi, @samuelcolvin, @miss-islington, @tirkarthi
PRs	bpo-38431: fix dataclasses.InitVar.__repr__ #16700 bpo-38431: Support non-class types in InitVar. #16701 bpo-38431: fix dataclasses.InitVar.__repr__ #16702 [3.8] bpo-38431: Fix __repr__ method of InitVar to work with typing objects. (GH-16702) #16744

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

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2019-10-13.12:50:54.195>
created_at = <Date 2019-10-10.15:31:02.114>
labels = ['3.8', 'type-bug', 'library']
title = 'dataclasses.InitVar breaks with typing.Optional'
updated_at = <Date 2019-10-13.12:50:54.193>
user = 'https://github.com/samuelcolvin'

bugs.python.org fields:

activity = <Date 2019-10-13.12:50:54.193>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2019-10-13.12:50:54.195>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2019-10-10.15:31:02.114>
creator = 'samuelcolvin'
dependencies = []
files = []
hgrepos = []
issue_num = 38431
keywords = ['patch', '3.8regression']
message_count = 7.0
messages = ['354388', '354389', '354390', '354392', '354574', '354576', '354578']
nosy_count = 6.0
nosy_names = ['eric.smith', 'serhiy.storchaka', 'levkivskyi', 'samuelcolvin', 'miss-islington', 'xtreak']
pr_nums = ['16700', '16701', '16702', '16744']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38431'
versions = ['Python 3.8']

[samuelcolvin]

The following code works fine with python 3.7 but breaks with 3.8:

import dataclasses
from typing import Optional

@dataclasses.dataclass
class TestingDataclass:
    base_path: dataclasses.InitVar[Optional[str]] = None

Exception traceback:

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    class TestingDataclass:
  File "/usr/local/lib/python3.8/dataclasses.py", line 995, in dataclass
    return wrap(cls)
  File "/usr/local/lib/python3.8/dataclasses.py", line 987, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen)
  File "/usr/local/lib/python3.8/dataclasses.py", line 967, in _process_class
    str(inspect.signature(cls)).replace(' -> None', ''))
  File "/usr/local/lib/python3.8/inspect.py", line 3050, in __str__
    formatted = str(param)
  File "/usr/local/lib/python3.8/inspect.py", line 2568, in __str__
    formatannotation(self._annotation))
  File "/usr/local/lib/python3.8/inspect.py", line 1202, in formatannotation
    return repr(annotation)
  File "/usr/local/lib/python3.8/dataclasses.py", line 213, in __repr__
    return f'dataclasses.InitVar[{self.type.__name__}]'
  File "/usr/local/lib/python3.8/typing.py", line 757, in __getattr__
    raise AttributeError(attr)
AttributeError: __name__

The code runs fine with str instead of Optional[str].

Tested locally with Python 3.8.0rc1 (tags/v3.8.0rc1:34214de6ab, Oct 10 2019, 16:15:14). The same error can be seen (in a more involved context) on travis here

[samuelcolvin]

This is a bug with the __repr__ method on InitVar.

I'm working on a PR now.

[tirkarthi]

git blame points to 01ee12b . I am tagging this as a 3.8 regression since the commit was not backported and 3.7 works fine. Feel free to remove it if it's a mistake.

[serhiy-storchaka]

Oh, Samuel already made a PR. Then I withdraw PR 16701.

[serhiy-storchaka]

New changeset 793cb85 by Serhiy Storchaka (Samuel Colvin) in branch 'master':
bpo-38431: Fix __repr__ method of InitVar to work with typing objects. (GH-16702)
793cb85

[miss-islington]

New changeset 6da52ac by Miss Islington (bot) in branch '3.8':
bpo-38431: Fix __repr__ method of InitVar to work with typing objects. (GH-16702)
6da52ac

[serhiy-storchaka]

Thank you for your contribution Samuel!