address review comments

Author: eendebakpt

Lib/dataclasses.py

@@ -1395,9 +1395,9 @@ def _field_names(class_or_instance):
 
     Accepts a dataclass or an instance of one. Excludes pseudo-fields.
     """
-
     return getattr(class_or_instance, _FIELD_NAMES)
 
+
 def _is_dataclass_instance(obj):
     """Returns True if obj is an instance of a dataclass."""
     return hasattr(type(obj), _FIELDS)

Misc/NEWS.d/next/Library/2025-08-29-17-58-36.gh-issue-138232.-W4iaS.rst

@@ -1 +1 @@
-Improve performance of :func:`dataclasses.asdict` up to 40%.
+Improve performance of :func:`dataclasses.asdict` up to 40% by caching the field names on dataclass classes.