[ty] introduce local variables for from imports of submodules in __init__.py(i)
#21173
+614
−185
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Diagnostic diff on typing conformance testsChanges were detected when running ty on typing conformance tests--- old-output.txt 2025-11-05 14:53:56.780666414 +0000
+++ new-output.txt 2025-11-05 14:54:00.083684704 +0000
@@ -1,4 +1,4 @@
-fatal[panic] Panicked at /home/runner/.cargo/git/checkouts/salsa-e6f3bb7c2a062968/664750a/src/function/execute.rs:464:17 when checking `/home/runner/work/ruff/ruff/typing/conformance/tests/aliases_typealiastype.py`: `infer_definition_types(Id(18af5)): execute: too many cycle iterations`
+fatal[panic] Panicked at /home/runner/.cargo/git/checkouts/salsa-e6f3bb7c2a062968/664750a/src/function/execute.rs:464:17 when checking `/home/runner/work/ruff/ruff/typing/conformance/tests/aliases_typealiastype.py`: `infer_definition_types(Id(18b08)): execute: too many cycle iterations`
_directives_deprecated_library.py:15:31: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `int`
_directives_deprecated_library.py:30:26: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `str`
_directives_deprecated_library.py:36:41: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `Self@__add__` |
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Contributor
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| Lint rule | Added | Removed | Changed |
|---|---|---|---|
unresolved-attribute |
6 | 612 | 10 |
invalid-assignment |
7 | 0 | 0 |
invalid-argument-type |
2 | 1 | 0 |
unused-ignore-comment |
3 | 0 | 0 |
unresolved-import |
0 | 2 | 0 |
call-non-callable |
1 | 0 | 0 |
possibly-missing-import |
1 | 0 | 0 |
possibly-unresolved-reference |
0 | 1 | 0 |
| Total | 20 | 616 | 10 |
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Preserving for future comparison: this is the "submodule-attributes" approach's results. I am now pushing up a different WIP implementation. 
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CodSpeed Performance ReportMerging #21173 will not alter performanceComparing Summary
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Just FYI, you can also access the full history here, I do that quite often after pushing a change. 
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I have cleaned up the implementation and added some more tests. I've made a few edge-cases a bit more strict. I am hoping this is a complete implementation, except for some code/mdtest comments need to be updated to reflect the current semantics. For posterity, this is the results that we agreed seemed shippable before my cleanup. Hopefully the stricter implementation isn't a huge change! 
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I believe the TL;DR of this PR is now:
As a reminder, "re-exported" is only an applicable concern for definitions in .pyi files, so both kinds of definitions will be fully visible in .py files. |
Gankra
requested review from
AlexWaygood,
MichaReiser,
carljm,
dcreager and
sharkdp
as code owners
Gankra
changed the title
from..import effectsfrom imports of submodules in __init__.py(i)
This was referenced Nov 5, 2025
available_submodule_attributes should probably be considered last instead of first
astral-sh/ty#1488
Open
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See astral-sh/ty#133 (comment) for a list of followups that I am intentionally punting on in this PR (or the sea of references right above this comment...) |
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This rips out the previous implementation in favour of a new implementation with 3 rules:
froms are locals: a
from..importcan only define locals, it does not have globalside-effects. Specifically any submodule attribute
athat's implicitly introduced by eitherfrom .a import borfrom . import a as b(in an__init__.py(i)) is a local and not aglobal. If you do such an import at the top of a file you won't notice this. However if you do
such an import in a function, that means it will only be function-scoped (so you'll need to do
it in every function that wants to access it, making your code less sensitive to execution
order).
first from first serve: only the first
from..importin an__init__.py(i)that imports aparticular direct submodule of the current package introduces that submodule as a local.
Subsequent imports of the submodule will not introduce that local. This reflects the fact that
in actual python only the first import of a submodule (in the entire execution of the program)
introduces it as an attribute of the package. By "first" we mean "the first time in this scope
(or any parent scope)". This pairs well with the fact that we are specifically introducing a
local (as long as you don't accidentally shadow or overwrite the local).
dot re-exports:
from . import ain an__init__.pyiis considered a re-export ofa(equivalent to
from . import a as a). This is required to properly handle many stubs in thewild. Currently it must be exactly
from . import ....This implementation is intentionally limited/conservative (notably, often requiring a from import to be relative). I'm going to file a ton of followups for improvements so that their impact can be evaluated separately.
Fixes astral-sh/ty#133