typing.get_type_hints() raises TypeError for a variable annotated by dataclasses.InitVar

@ericvsmith

BPO	44799
Nosy	@ericvsmith, @JelleZijlstra, @uriyyo, @tk0miya
PRs	bpo-44799: Fix InitVar resolving using get_type_hints #27553

^{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 = 'https://github.com/ericvsmith'
closed_at = <Date 2022-03-12.18:00:32.186>
created_at = <Date 2021-07-31.17:19:44.535>
labels = ['library', '3.9', '3.10']
title = 'typing.get_type_hints() raises TypeError for a variable annotated by dataclasses.InitVar'
updated_at = <Date 2022-03-12.18:00:32.185>
user = 'https://github.com/tk0miya'

bugs.python.org fields:

activity = <Date 2022-03-12.18:00:32.185>
actor = 'JelleZijlstra'
assignee = 'eric.smith'
closed = True
closed_date = <Date 2022-03-12.18:00:32.186>
closer = 'JelleZijlstra'
components = ['Library (Lib)']
creation = <Date 2021-07-31.17:19:44.535>
creator = 'tkomiya'
dependencies = []
files = []
hgrepos = []
issue_num = 44799
keywords = ['patch']
message_count = 4.0
messages = ['398650', '411228', '414969', '414974']
nosy_count = 4.0
nosy_names = ['eric.smith', 'JelleZijlstra', 'uriyyo', 'tkomiya']
pr_nums = ['27553']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue44799'
versions = ['Python 3.9', 'Python 3.10']

I found typing.get_type_hints() raises TypeError for a variable annotated by dataclasses.InitVar when lazy annotations evaluation-feature is enabled (a.k.a __future__.annotations).

$ cat test.py
from __future__ import annotations
from dataclasses import dataclass, InitVar
from typing import get_type_hints

@dataclass
class Foo:
    attr: InitVar[int]


get_type_hints(Foo)

$ python -V
Python 3.9.6
$ python test.py
Traceback (most recent call last):
  File "/Users/tkomiya/work/sphinx/test.py", line 10, in <module>
    get_type_hints(Foo)
  File "/Users/tkomiya/.pyenv/versions/3.9.6/lib/python3.9/typing.py", line 1424, in get_type_hints
    value = _eval_type(value, base_globals, localns)
  File "/Users/tkomiya/.pyenv/versions/3.9.6/lib/python3.9/typing.py", line 290, in _eval_type
    return t._evaluate(globalns, localns, recursive_guard)
  File "/Users/tkomiya/.pyenv/versions/3.9.6/lib/python3.9/typing.py", line 545, in _evaluate
    type_ =_type_check(
  File "/Users/tkomiya/.pyenv/versions/3.9.6/lib/python3.9/typing.py", line 164, in _type_check
    raise TypeError(f"{msg} Got {arg!r:.100}.")
TypeError: Forward references must evaluate to types. Got dataclasses.InitVar[int].

It goes well if lazy annotations evaluation is disabled.

I think this should be fixed in typing.py instead. get_type_hints() should be less strict about what it accepts as a type, so users are free to use annotations in innovative ways.

Static type checkers should have the job of enforcing that type annotations are valid types.

This is now fixed in main thanks to bpo-46644:

>>> get_type_hints(Foo)
{'attr': dataclasses.InitVar[int]}

We're not backporting that change to the bugfix branches. If we want to fix this issue in 3.10 and 3.9, we'll have to add a __call__ method to InitVar. My inclination is that that's not worth it.

I agree it's not worth fixing in 3.9 and 3.10.

Navigation Menu

Repository navigation

typing.get_type_hints() raises TypeError for a variable annotated by dataclasses.InitVar #88962

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

typing.get_type_hints() raises TypeError for a variable annotated by dataclasses.InitVar #88962

Description

Activity

tk0miya commented on Jul 31, 2021

JelleZijlstra commented on Jan 22, 2022

JelleZijlstra commented on Mar 12, 2022

ericvsmith commented on Mar 12, 2022

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions