https://github.com/python/cpython/commit/0a39730ecd45430e14cfeb244980b6eaa3571695 commit: 0a39730ecd45430e14cfeb244980b6eaa3571695 branch: main author: Daniel Hollas <[email protected]> committer: JelleZijlstra <[email protected]> date: 2026-04-25T22:57:38-07:00 summary:
gh-137855: Lazy import `inspect` module in dataclasses (#144387) Co-authored-by: Hugo van Kemenade <[email protected]> files: A Misc/NEWS.d/next/Library/2026-02-12-18-05-16.gh-issue-137855.2_PTbg.rst M Lib/dataclasses.py M Lib/test/test__colorize.py M Lib/test/test_dataclasses/__init__.py diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py index 988edfed6f4dcb..df192763c5bd15 100644 --- a/Lib/dataclasses.py +++ b/Lib/dataclasses.py @@ -1,12 +1,12 @@ import sys import types -import inspect import keyword import itertools import annotationlib import abc from reprlib import recursive_repr lazy import copy +lazy import inspect lazy import re @@ -988,6 +988,28 @@ def _hash_exception(cls, fields, func_builder): # See https://bugs.python.org/issue32929#msg312829 for an if-statement # version of this table. +# A non-data descriptor to autogenerate class docstring +# from the signature of its __init__ method on demand. +# The primary reason is to be able to lazy import `inspect` module. +class _AutoDocstring: + + def __get__(self, _obj, cls): + try: + # In some cases fetching a signature is not possible. + # But, we surely should not fail in this case. + text_sig = str(inspect.signature( + cls, + annotation_format=annotationlib.Format.FORWARDREF, + )).replace(' -> None', '') + except TypeError, ValueError: + text_sig = '' + + doc = cls.__name__ + text_sig + setattr(cls, '__doc__', doc) + return doc + +_auto_docstring = _AutoDocstring() + def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen, match_args, kw_only, slots, weakref_slot): @@ -1215,23 +1237,13 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen, if hash_action: cls.__hash__ = hash_action(cls, field_list, func_builder) - # Generate the methods and add them to the class. This needs to be done - # before the __doc__ logic below, since inspect will look at the __init__ - # signature. + # Generate the methods and add them to the class. func_builder.add_fns_to_class(cls) if not getattr(cls, '__doc__'): - # Create a class doc-string. - try: - # In some cases fetching a signature is not possible. - # But, we surely should not fail in this case. - text_sig = str(inspect.signature( - cls, - annotation_format=annotationlib.Format.FORWARDREF, - )).replace(' -> None', '') - except (TypeError, ValueError): - text_sig = '' - cls.__doc__ = (cls.__name__ + text_sig) + # Create a class doc-string lazily via descriptor protocol + # to avoid importing `inspect` module. + cls.__doc__ = _auto_docstring if match_args: # I could probably compute this once. @@ -1391,8 +1403,10 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields): # make an update, since all closures for a class will share a # given cell. for member in newcls.__dict__.values(): + # If this is a wrapped function, unwrap it. - member = inspect.unwrap(member) + if not isinstance(member, type) and hasattr(member, '__wrapped__'): + member = inspect.unwrap(member) if isinstance(member, types.FunctionType): if _update_func_cell_for__class__(member, cls, newcls): diff --git a/Lib/test/test__colorize.py b/Lib/test/test__colorize.py index 0353ff7530b92a..48fa52bfd5672c 100644 --- a/Lib/test/test__colorize.py +++ b/Lib/test/test__colorize.py @@ -28,7 +28,7 @@ class TestImportTime(unittest.TestCase): @cpython_only def test_lazy_import(self): import_helper.ensure_lazy_imports( - "_colorize", {"copy", "re"} + "_colorize", {"copy", "re", "inspect"} ) diff --git a/Lib/test/test_dataclasses/__init__.py b/Lib/test/test_dataclasses/__init__.py index 6ff82b8810abed..5eec9e23cd414b 100644 --- a/Lib/test/test_dataclasses/__init__.py +++ b/Lib/test/test_dataclasses/__init__.py @@ -27,11 +27,21 @@ import dataclasses # Needed for the string "dataclasses.InitVar[int]" to work as an annotation. from test import support -from test.support import import_helper +from test.support import cpython_only, import_helper # Just any custom exception we can catch. class CustomError(Exception): pass + +class TestImportTime(unittest.TestCase): + + @cpython_only + def test_lazy_import(self): + import_helper.ensure_lazy_imports( + "dataclasses", {"inspect", "re", "copy"} + ) + + class TestCase(unittest.TestCase): def test_no_fields(self): @dataclass @@ -2309,6 +2319,20 @@ class C: self.assertDocStrEqual(C.__doc__, "C()") + def test_docstring_slotted(self): + @dataclass(slots=True) + class C: + x: int + + self.assertDocStrEqual(C.__doc__, "C(x:int)") + + def test_docstring_recursive(self): + @dataclass() + class C: + x: list[C] + + self.assertDocStrEqual(C.__doc__, "C(x:list[test.test_dataclasses.TestDocString.test_docstring_recursive.<locals>.C])") + def test_docstring_one_field(self): @dataclass class C: diff --git a/Misc/NEWS.d/next/Library/2026-02-12-18-05-16.gh-issue-137855.2_PTbg.rst b/Misc/NEWS.d/next/Library/2026-02-12-18-05-16.gh-issue-137855.2_PTbg.rst new file mode 100644 index 00000000000000..586c7d3495ae26 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-02-12-18-05-16.gh-issue-137855.2_PTbg.rst @@ -0,0 +1 @@ +Reduce the import time of :mod:`dataclasses` module by ~20%. _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
