Repository navigation
test_concurrent_lazy_import_reification is flaky #154561
Description
Bug report
Bug description:
See for example, this run:
======================================================================
FAIL: test_concurrent_lazy_import_reification (test.test_lazy_import.ThreadSafetyTests.test_concurrent_lazy_import_reification)
Multiple threads racing to reify the same lazy import should succeed.
----------------------------------------------------------------------
Traceback (most recent call last):
File "/var/lib/buildbot/workers/rise-riscv64-3/3.x.rise-riscv64-3.nogil/build/Lib/test/test_lazy_import/__init__.py", line 1820, in test_concurrent_lazy_import_reification
self.assertEqual(errors, [], f"Errors occurred: {errors}")
~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: Lists differ: [(9, AttributeError("module 'test.test_laz[39 chars]'"))] != []
First list contains 1 additional elements.
First extra element 0:
(9, AttributeError("module 'test.test_lazy_import.data' has no attribute 'basic2'"))
+ []
- [(9,
- AttributeError("module 'test.test_lazy_import.data' has no attribute 'basic2'"))] : Errors occurred: [(9, AttributeError("module 'test.test_lazy_import.data' has no attribute 'basic2'"))]
----------------------------------------------------------------------
Ran 128 tests in 78.334s
FAILED (failures=1)
test test_lazy_import failed
CPython versions tested on:
CPython main branch
Operating systems tested on:
No response
Activity
johnslavik commentedon Jul 23, 2026
@pablogsal
johnslavik commentedon Jul 23, 2026
Oh, I thought this was new but it's an old one. I'll try to work on this. I reproduced it locally.
BHUVANSH855 commentedon Jul 24, 2026
Hi! I've been investigating the intermittent failure in
test_concurrent_lazy_import_reificationand have been able to reproduce it locally.So far I've instrumented both the C and Python sides of the lazy import path. Here's what I've observed:
setattr(parent_module, child, module)succeeds, and an immediateassert getattr(parent_module, child) is modulealways passes._find_and_load_lazy_submodule()is just a wrapper around_find_and_load(..., lazy_submodule=True)._find_and_load_unlocked()publishes the child module on the parent and doesn't appear to remove it afterwards.has_key=0,contains=1),AttributeError, and by then the pending-set entry is already gone (contains=0).At this point I'm not seeing any Python-level code that removes the published attribute after
setattr(), so I'm wondering if I'm looking in the wrong place.Would you recommend continuing to investigate the free-threaded module attribute implementation / synchronization, or is there another part of the lazy import implementation that would be a better place to look?
brittanyrey commentedon Sep 18, 2026
This no longer repros.
It looks like it was fixed when the fix for #155194 went in.
cc: @johnslavik to close
Fix free-threaded race reifying a lazy submodule attribute
johnslavik commentedon Sep 18, 2026
I've stress-tested the test under a higher number of threads and confirm this no longer reproduces. Thank you @brittanyrey!
lazy import math.pi#155194