When re-importing a submodule lazily after removing it, it's never added back to sys.modules.

[brittanyrey]

Bug report

Bug description:

While working on setting up testing infra for lazy_imports=all, I came across this test failure in test_trace. It appears that after importing a submodule, deleting said submodule, and then lazy importing it again--the module doesn't make it's way back into sys.modules.

Example failing code snippet:

import sys
modname = "test.test_lazy_import.data.pkg.bar"
import test.test_lazy_import.data.pkg.bar
del sys.modules[modname]
lazy import test.test_lazy_import.data.pkg.bar  # the issue is also seen when using lazy from
bar.f()
assert modname in sys.modules  # False

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-151408: Re-register submodules in sys.modules on lazy re-import #151411
• gh-151408: Fix bug with lazy importing a previously imported and removed module #151412

[bhuvi27]

I'm working on a fix for this.

[brittanyrey]

@bhuvi27 I have one already

[vstinner]

I'm working on a fix for this.

It's usually kind to ask the reporter if they want to work on a fix.

[brittanyrey]

cc fellow lazy imports folks: @DinoV @Yhg1s @pablogsal

[brittanyrey]

This issue no longer reproduces on main but, it continues to fail on 3.15. I dug into it a bit & I think @DinoV's fix #155189 addressed the issue. We just need the back port for 3.15--I'm glad to toss it together if it's not already in progress.

Sample Snippets:

Python 3.16.0a0 (heads/main:a7bb524fef6, Aug 17 2026, 20:00:54) [GCC 11.5.0 20240719 (Red Hat 11.5.0-15)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> modname = "test.test_lazy_import.data.pkg.bar"
>>> import test.test_lazy_import.data.pkg.bar
BAR_MODULE_LOADED
>>> del sys.modules[modname]
>>> lazy import test.test_lazy_import.data.pkg.bar
>>> test.test_lazy_import.data.pkg.bar.f()
BAR_MODULE_LOADED
>>> assert modname in sys.modules

Python 3.15.0rc1+dev (heads/3.15:ac4e5d2108c, Aug 17 2026, 19:54:52) [GCC 11.5.0 20240719 (Red Hat 11.5.0-15)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> modname = "test.test_lazy_import.data.pkg.bar"
>>> import test.test_lazy_import.data.pkg.bar
BAR_MODULE_LOADED
>>> del sys.modules[modname]
>>> lazy import test.test_lazy_import.data.pkg.bar
>>> test.test_lazy_import.data.pkg.bar.f()
>>> assert modname in sys.modules
Traceback (most recent call last):
  File "<python-input-6>", line 1, in <module>
    assert modname in sys.modules
           ^^^^^^^^^^^^^^^^^^^^^^
AssertionError

NOTE: also calling the method doesn't produce the second print message in the 3.15 version..