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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Mypy subclass/intersection issue on 1.15.0","articleBody":"This code filters using an `isinstance` call to try to find objects that fit the profile of both `Foo` and `Bar`:\r\n\r\n```python\r\nfrom abc import ABC\r\nfrom collections.abc import Sequence\r\n\r\nclass Foo(ABC):\r\n    pass\r\n\r\nclass Bar(ABC):\r\n    pass\r\n\r\nclass Baz(ABC):\r\n    pass\r\n\r\nclass FooBar(Foo, Bar):\r\n    pass\r\n\r\nclass FooBaz(Foo, Baz):\r\n    pass\r\n\r\ndef my_func(foos: list[Foo]) -\u003e Sequence[Foo]:\r\n    my_list = []\r\n    for foo in foos:\r\n        if not isinstance(foo, Bar):\r\n            continue\r\n        my_list.append(foo)\r\n    return my_list\r\n\r\nfoos = [FooBar(), FooBaz()]\r\nmy_func(foos)\r\n```\r\n\r\nThis code does not fail on Mypy 1.14.1:\r\n\r\nhttps://mypy-play.net/?mypy=1.14.1\u0026python=3.12\u0026gist=7b5be66ab0fb3f04d15a99317ef21a7d\r\n\r\nBut it does fail on Mypy 1.15:\r\n\r\n```\r\nmain.py:24: error: Argument 1 to \"append\" of \"list\" has incompatible type \"__main__.\u003csubclass of \"Foo\" and \"Bar\"\u003e1\"; expected \"__main__.\u003csubclass of \"Foo\" and \"Bar\"\u003e\"  [arg-type]\r\nFound 1 error in 1 file (checked 1 source file)\r\n```\r\n\r\nhttps://mypy-play.net/?mypy=1.15.0\u0026python=3.12\u0026gist=7b5be66ab0fb3f04d15a99317ef21a7d\r\n\r\n_Originally posted by @gandhis1 in https://github.com/python/typing/discussions/1968_","author":{"url":"https://github.com/gandhis1","@type":"Person","name":"gandhis1"},"datePublished":"2025-04-12T12:47:14.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/18912/mypy/issues/18912"}