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Mypy subclass/intersection issue on 1.15.0 #18912
Description
This code filters using an isinstance call to try to find objects that fit the profile of both Foo and Bar:
from abc import ABC
from collections.abc import Sequence
class Foo(ABC):
pass
class Bar(ABC):
pass
class Baz(ABC):
pass
class FooBar(Foo, Bar):
pass
class FooBaz(Foo, Baz):
pass
def my_func(foos: list[Foo]) -> Sequence[Foo]:
my_list = []
for foo in foos:
if not isinstance(foo, Bar):
continue
my_list.append(foo)
return my_list
foos = [FooBar(), FooBaz()]
my_func(foos)This code does not fail on Mypy 1.14.1:
https://mypy-play.net/?mypy=1.14.1&python=3.12&gist=7b5be66ab0fb3f04d15a99317ef21a7d
But it does fail on Mypy 1.15:
main.py:24: error: Argument 1 to "append" of "list" has incompatible type "__main__.<subclass of "Foo" and "Bar">1"; expected "__main__.<subclass of "Foo" and "Bar">" [arg-type]
Found 1 error in 1 file (checked 1 source file)
https://mypy-play.net/?mypy=1.15.0&python=3.12&gist=7b5be66ab0fb3f04d15a99317ef21a7d
Originally posted by @gandhis1 in python/typing#1968
Activity
sterliakov commentedon Apr 13, 2025
This is the problem discussed in #18433 -
pyodidefalse positive caused by incompatible pseudo-intersections.gandhis1 commentedon Apr 14, 2025
I realized I did not check the
masterbranch, and it appears this issue is fixed onmaster: https://mypy-play.net/?mypy=master&python=3.12&gist=7b5be66ab0fb3f04d15a99317ef21a7d