From 57db12514ac686f0a752ec8fe1c08b6daa0c6219 Mon Sep 17 00:00:00 2001 From: Amer Esmail Elsheikh Date: Fri, 12 Dec 2025 22:26:50 +0200 Subject: [PATCH] gh-139686: Make reloading a lazy module no-op (GH-139857) Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com> Co-authored-by: Brett Cannon --- Doc/library/importlib.rst | 6 +++++ Lib/importlib/__init__.py | 5 ++++ Lib/test/test_importlib/test_lazy.py | 25 ++++++++++++++++++- ...-10-09-15-46-18.gh-issue-139686.XwIZB2.rst | 1 + 4 files changed, 36 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Library/2025-10-09-15-46-18.gh-issue-139686.XwIZB2.rst diff --git a/Doc/library/importlib.rst b/Doc/library/importlib.rst index c5ea78c16837..b04403cd15a5 100644 --- a/Doc/library/importlib.rst +++ b/Doc/library/importlib.rst @@ -210,6 +210,12 @@ Functions :exc:`ModuleNotFoundError` is raised when the module being reloaded lacks a :class:`~importlib.machinery.ModuleSpec`. + .. versionchanged:: 3.14 + If *module* is a lazy module that has not yet been materialized (i.e., + loaded via :class:`importlib.util.LazyLoader` and not yet accessed), + calling :func:`reload` is a no-op and returns the module unchanged. + This prevents the reload from unintentionally triggering the lazy load. + .. warning:: This function is not thread-safe. Calling it from multiple threads can result in unexpected behavior. It's recommended to use the :class:`threading.Lock` diff --git a/Lib/importlib/__init__.py b/Lib/importlib/__init__.py index a7d57561ead0..694fea806f79 100644 --- a/Lib/importlib/__init__.py +++ b/Lib/importlib/__init__.py @@ -97,6 +97,11 @@ def reload(module): The module must have been successfully imported before. """ + # If a LazyModule has not yet been materialized, reload is a no-op. + if importlib_util := sys.modules.get('importlib.util'): + if lazy_module_type := getattr(importlib_util, '_LazyModule', None): + if isinstance(module, lazy_module_type): + return module try: name = module.__spec__.name except AttributeError: diff --git a/Lib/test/test_importlib/test_lazy.py b/Lib/test/test_importlib/test_lazy.py index e48fad8898f0..c6b26ad75b97 100644 --- a/Lib/test/test_importlib/test_lazy.py +++ b/Lib/test/test_importlib/test_lazy.py @@ -10,6 +10,9 @@ import unittest from test.support import threading_helper from test.test_importlib import util as test_util +# Make sure sys.modules[util] is in sync with the import. +# That is needed as other tests may reload util. +sys.modules['importlib.util'] = util class CollectInit: @@ -192,7 +195,7 @@ class LazyLoaderTests(unittest.TestCase): sys.modules['json'] = module loader.exec_module(module) - # Trigger load with attribute lookup, ensure expected behavior + # Trigger load with attribute lookup, ensure expected behavior. test_load = module.loads('{}') self.assertEqual(test_load, {}) @@ -224,6 +227,26 @@ sys.modules[__name__].__class__ = ImmutableModule with self.assertRaises(AttributeError): del module.CONSTANT + def test_reload(self): + # Reloading a lazy module that hasn't been materialized is a no-op. + module = self.new_module() + sys.modules[TestingImporter.module_name] = module + + # Change the source code to add a new attribute. + TestingImporter.source_code = 'attr = 42\nnew_attr = 123\n__name__ = {!r}'.format(TestingImporter.mutated_name) + self.assertIsInstance(module, util._LazyModule) + + # Reload the module (should be a no-op since not materialized). + reloaded = importlib.reload(module) + self.assertIs(reloaded, module) + self.assertIsInstance(module, util._LazyModule) + + # Access the new attribute (should trigger materialization, and new_attr should exist). + self.assertEqual(module.attr, 42) + self.assertNotIsInstance(module, util._LazyModule) + self.assertTrue(hasattr(module, 'new_attr')) + self.assertEqual(module.new_attr, 123) + if __name__ == '__main__': unittest.main() diff --git a/Misc/NEWS.d/next/Library/2025-10-09-15-46-18.gh-issue-139686.XwIZB2.rst b/Misc/NEWS.d/next/Library/2025-10-09-15-46-18.gh-issue-139686.XwIZB2.rst new file mode 100644 index 000000000000..00dd3447eebb --- /dev/null +++ b/Misc/NEWS.d/next/Library/2025-10-09-15-46-18.gh-issue-139686.XwIZB2.rst @@ -0,0 +1 @@ +Make importlib.reload no-op for lazy modules. -- 2.47.3