dataclasses.replace raises an exception if InitVar with default argument is not provided.

[GregKuhn]

BPO	36470
Nosy	@ericvsmith, @ilevkivskyi, @ZackerySpytz, @miss-islington, @mierzejk, @anthrotype
PRs	bpo-36470: Allow dataclasses.replace() to work InitVar with default values #17441 bpo-36470: Allow dataclasses.replace() to handle InitVars with default values #20867 [3.9] bpo-36470: Allow dataclasses.replace() to handle InitVars with default values (GH-20867) #25200 [3.8] bpo-36470: Allow dataclasses.replace() to handle InitVars with default values (GH-20867) #25201

^{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/ericvsmith'
closed_at = <Date 2021-04-05.20:12:35.465>
created_at = <Date 2019-03-29.11:52:18.656>
labels = ['interpreter-core', 'type-bug', '3.7']
title = 'dataclasses.replace raises an exception if InitVar with default argument is not provided.'
updated_at = <Date 2021-04-05.20:12:35.464>
user = 'https://bugs.python.org/GregKuhn'

bugs.python.org fields:

activity = <Date 2021-04-05.20:12:35.464>
actor = 'eric.smith'
assignee = 'eric.smith'
closed = True
closed_date = <Date 2021-04-05.20:12:35.465>
closer = 'eric.smith'
components = ['Interpreter Core']
creation = <Date 2019-03-29.11:52:18.656>
creator = 'Greg Kuhn'
dependencies = []
files = []
hgrepos = []
issue_num = 36470
keywords = ['patch']
message_count = 7.0
messages = ['339105', '339124', '385914', '390252', '390256', '390257', '390259']
nosy_count = 7.0
nosy_names = ['eric.smith', 'levkivskyi', 'ZackerySpytz', 'miss-islington', 'Greg Kuhn', 'mierzej', 'anthrotype']
pr_nums = ['17441', '20867', '25200', '25201']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue36470'
versions = ['Python 3.7']

[GregKuhn]

I have a snippet below which runs fine on python 3.7.0 but raises a ValueError exception on 3.7.1. I believe it's related to https://bugs.python.org/issue33805.

The error: c:\python\lib\dataclasses.py:1219: ValueError

The script:

from dataclasses import replace, dataclass, InitVar

@dataclass
class Test:
    a:int = 1
    b:InitVar[int] = None

    def __post_init__(self, b):
        if b is not None:
            self.a = b


if __name__ == '__main__':
    t = Test()
    t1 = Test(b=5)
    assert t1.a == 5

    t2 = replace(t1, **{})
    print(t2)

[GregKuhn]

Fixed title

[anthrotype]

any updates on this? Would be great if any of the two candidate PRs was merged. It's basically impossible to use replace() with default InitVars..
Thank you in advace

[miss-islington]

New changeset 7522067 by Zackery Spytz in branch 'master':
bpo-36470: Allow dataclasses.replace() to handle InitVars with default values (GH-20867)
7522067

[ericvsmith]

New changeset bdee2a3 by Miss Islington (bot) in branch '3.8':
bpo-36470: Allow dataclasses.replace() to handle InitVars with default values (GH-20867) (GH-25201)
bdee2a3

[ericvsmith]

New changeset 013c30e by Miss Islington (bot) in branch '3.9':
bpo-36470: Allow dataclasses.replace() to handle InitVars with default values (GH-20867) (GH-25200)
013c30e

[ericvsmith]

Thanks for the fix!