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GeezerVison is showing github.com — gh-89687: fix get_type_hints with dataclasses __init__ generation by Tishka17 · Pull Request #137168 · python/cpython

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@Tishka17

@Tishka17 Tishka17 commented Jul 28, 2025 •
edited by bedevere-app Bot
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Fixes for #89687
Based on original #29158

  • Issue: Cross-module dataclass inheritance breaks get_type_hints #89687

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@Tishka17
Tishka17 requested a review from ericvsmith as a code owner July 28, 2025 14:18
@python-cla-bot

python-cla-bot Bot commented Jul 28, 2025 •
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All commit authors signed the Contributor License Agreement.

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@bedevere-app bedevere-app Bot added the awaiting review label Jul 28, 2025
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bedevere-app Bot commented Jul 28, 2025

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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.
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@bedevere-app bedevere-app Bot mentioned this pull request Jul 28, 2025
Cross-module dataclass inheritance breaks get_type_hints #89687
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@Tishka17
Tishka17 force-pushed the issue-45524 branch from bef5cf2 to 3a449ba Compare July 28, 2025 14:32
@Tishka17
pythongh-89687: fix get_type_hints with dataclasses __init__ generation
132c74b
@Tishka17
Tishka17 force-pushed the issue-45524 branch from 3a449ba to 132c74b Compare July 28, 2025 14:39
@Tishka17

Tishka17 commented Jul 28, 2025

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As I see at this point:

  1. annotationlib.get_annotations does not resolve ForwardRef at all
  2. typing.get_type_hints ignores module in ForwardRef
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@Tishka17
Fix using forward module in ForwardRef
3ff28d2
@Tishka17
Tishka17 requested a review from JelleZijlstra as a code owner July 28, 2025 15:58
JelleZijlstra
JelleZijlstra reviewed Jul 28, 2025
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Comment thread Lib/annotationlib.py

arg = self.__forward_arg__
if arg.isidentifier() and not keyword.iskeyword(arg):
if self.__forward_module__ is not None:

@JelleZijlstra JelleZijlstra Jul 28, 2025

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I don't think this is correct, since we infer globals from __forward_module__ if no explicit globals are given. And if explicit globals are given, we shouldn't be using __forward_module__.

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@Tishka17 Tishka17 Jul 28, 2025

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I don't think current behavior is correct. Was there any discussion?

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JelleZijlstra
JelleZijlstra reviewed Jul 30, 2025
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Comment thread Lib/dataclasses.py
# Return the text of the line in the body of __init__ that will
# initialize this field.

if f.init and isinstance(f.type, str):

@JelleZijlstra JelleZijlstra Jul 30, 2025

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Something like this is good, but I'd do it like this:

diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 53b3b54cfb3..e3d25fb0840 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -789,7 +789,10 @@ def _get_field(cls, a_name, a_type, default_kw_only):
 
     # Only at this point do we know the name and the type.  Set them.
     f.name = a_name
-    f.type = a_type
+    if isinstance(a_type, str):
+        f.type = annotationlib.ForwardRef(a_type, owner=cls)
+    else:
+        f.type = a_type
 
     # Assume it's a normal field until proven otherwise.  We're next
     # going to decide if it's a ClassVar or InitVar, everything else

ForwardRef now lives in annotationlib, not typing. There's no need to catch SyntaxError as it doesn't parse its input in the constructor.

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@github-actions

github-actions Bot commented Apr 27, 2026

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This PR is stale because it has been open for 30 days with no activity.
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@github-actions github-actions Bot added the stale Stale PR or inactive for long period of time. label Apr 27, 2026
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@JelleZijlstra JelleZijlstra JelleZijlstra left review comments
@ericvsmith ericvsmith Awaiting requested review from ericvsmith ericvsmith is a code owner

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@Tishka17 @JelleZijlstra
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