Identical, anonymous intersection types causes incompatible import [assignment] error when imported via *
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Description
Bug Report
If you import * from two modules that infer an identical intersection type, mypy will report an error along the lines of
Incompatible import of "<intersection>" (imported name has type "type[a.<intersection>]", local name has type "type[b.<intersection>]") [assignment]
To Reproduce
This repro requires multiple files. They are delineated by comments.
# shared.py
class Foo: ...
class Bar: ...
# a.py
from shared import Foo, Bar
a_foos: list[Foo]
a_bars = [f for f in a_foos if isinstance(f, Bar)]
# b.py
from shared import Foo, Bar
b_foos: list[Foo]
b_bars = [f for f in b_foos if isinstance(f, Bar)]
# c.py
from a import *
from b import *
The offending mypy invocation is as follows:
$ mypy -m c
Expected Behavior
This should not emit an error because no runtime locals are actually assigned, or at the very least, because the intersections are identical.
Actual Behavior
c.py:2: error: Incompatible import of "<subclass of "Foo" and "Bar">" (imported name has type "type[b.<subclass of "Foo" and "Bar">]", local name has type "type[a.<subclass of "Foo" and "Bar">]") [assignment]
Found 1 error in 1 file (checked 1 source file)
Your Environment
This bug was reproduced in a fresh venv on Debian GNU/Linux 10 (buster):
$ python --version
Python 3.10.13
$ mypy --version
mypy 1.6.0 (compiled: yes)
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Create the four files shown in the report: shared.py, a.py, b.py, and c.py, then run mypy -m c to reproduce the incompatible-import error. Trace star-import handling and the inferred anonymous intersection types; done means the identical intersections no longer produce an error while the repro still type-checks correctly.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100