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GeezerVison is showing github.com — [3.15] gh-155194: Fix not raising on non-module import by DinoV · Pull Request #155188 · python/cpython

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@DinoV

@DinoV DinoV commented Aug 4, 2026 •
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As initially reported here: https://discuss.python.org/t/sys-lazy-modules-clarification/108385

lazy import math.pi has divergent behavior from import math.pi. Currently we allow this to work and just give you the math module. Instead we should raise ModuleNotFoundError because math.pi is not a module.

This would be a breaking change in the future so starting w/ fixing it in 3.15 because fixing it only in later versions would probably be bad.

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@DinoV
Fix not raising on non-module import
69e82f2
@DinoV DinoV changed the title Fix not raising on non-module import gh-155194: Fix not raising on non-module import Aug 4, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Aug 4, 2026
lazy imports allow lazy import math.pi #155194
Closed
@DinoV DinoV added the skip news label Aug 4, 2026
@DinoV DinoV changed the title gh-155194: Fix not raising on non-module import [3.15] gh-155194: Fix not raising on non-module import Aug 4, 2026
@DinoV
DinoV requested a review from hugovk August 4, 2026 21:22
@DinoV
Fix traceback tests
7063fa2
@DinoV
DinoV force-pushed the lazy_fixes branch from 273069d to 7063fa2 Compare August 4, 2026 21:41
@DinoV
DinoV marked this pull request as ready for review August 4, 2026 22:49
@DinoV
DinoV requested review from AA-Turner, FFY00, Yhg1s, brettcannon, emmatyping, ericsnowcurrently, erlend-aasland, kumaraditya303, ncoghlan, pablogsal and warsaw as code owners August 4, 2026 22:49
@bedevere-app bedevere-app Bot added the awaiting core review label Aug 4, 2026
@DinoV DinoV added 3.15 bugs and security fixes topic-lazy-imports labels Aug 4, 2026
Yhg1s
Yhg1s reviewed Aug 5, 2026
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Comment thread Lib/test/test_lazy_import/__init__.py Outdated
assert_python_ok("-c", code)

def test_non_package_lazily_imported(self):
"""Accessing a nonexistent lazy submodule via parent attr raises AttributeError."""

@Yhg1s Yhg1s Aug 5, 2026

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Suggested change
"""Accessing a nonexistent lazy submodule via parent attr raises AttributeError."""
"""Accessing a nonexistent lazy submodule via parent attr raises ModuleNotFoundError."""

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Comment thread Python/import.c
);
Py_DECREF(name);
}
obj = _PyEval_ImportNameWithImport(

@Yhg1s Yhg1s Aug 5, 2026

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Hm, does this change the error for lazy from ... import nonexistent_attr? We don't seem to have explicit tests for what that raises, just the chaining test?

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@DinoV DinoV Aug 5, 2026

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Nope, that'll be the same. In the from case we're already doing a full import (it's probably not super clear here because that's when lz_attr is not NULL and that's maybe not the best name)

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@DinoV
Fix doc string and add new test
09e0325
@emmatyping

emmatyping commented Aug 5, 2026

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Is there a reason there is a 3.15 specific PR here rather than backporting the one targeting main once that's merged? #155189

If so, it might be good to explain that in the PR description.
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@DinoV

DinoV commented Aug 5, 2026

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Is there a reason there is a 3.15 specific PR here rather than backporting the one targeting main once that's merged? #155189

If so, it might be good to explain that in the PR description.

Mainly because if we don't fix it in 3.15 I don't think we should ever fix it - it would probably be a breaking change as people would come to depend upon it so I think we should fix it here first or not fix it at all.
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@Yhg1s

Yhg1s commented Aug 6, 2026

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Mainly because if we don't fix it in 3.15 I don't think we should ever fix it - it would probably be a breaking change as people would come to depend upon it so I think we should fix it here first or not fix it at all.

Let's get Hugo's opinion on getting this into the next RC then, and if he's okay with that, apply it to main first. (Doing things in the other direction makes future merges more awkward.) FWIW, I think this is such a clear corner case that I think it would be fine to change in 3.15.1 as well, but I'm not in charge :)
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@Yhg1s

Yhg1s commented Aug 6, 2026

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@hugovk ^
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@hugovk

hugovk commented Aug 6, 2026

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Yes, let's fix this for rc2, and do it in main first.
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pablogsal
pablogsal reviewed Aug 10, 2026
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Comment thread Lib/test/test_lazy_import/__init__.py Resolved

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Comment thread Lib/test/test_lazy_import/__init__.py Resolved

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Comment thread Lib/test/test_lazy_import/data/lazypkg/bar.py Resolved

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Comment thread Lib/test/test_lazy_import/__init__.py Resolved

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Comment thread Lib/test/test_lazy_import/data/lazypkg/bar.py Resolved

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Comment thread Lib/test/test_lazy_import/__init__.py
assert_python_ok("-c", code)

def test_non_package_lazily_imported(self):
"""Accessing a nonexistent lazy submodule via parent attr raises ModuleNotFoundError."""

@pablogsal pablogsal Aug 10, 2026

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Nit: math.pi is an existing non-module attribute, and sys.doesnotexist is a missing attribute rather than a submodule. Can we describe those cases directly?

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@DinoV DinoV Aug 10, 2026

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@pablogsal I've fixed up these in the main PR (#155189), I'm going to close this one per the discussion above.

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@DinoV DinoV closed this Aug 10, 2026
@DinoV DinoV mentioned this pull request Aug 14, 2026
gh-155194: Fix not raising on non-module import #155189
Merged
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@DinoV @emmatyping @Yhg1s @hugovk @pablogsal
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