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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Dict arguments that contain a subclass are not handled by Mypy correctly","articleBody":"I have the following example piece of code\r\n\r\n```\r\nfrom typing import Any, Dict\r\n\r\n\r\nclass P:\r\n    pass\r\n\r\nclass C(P):\r\n    pass\r\n\r\nclass A:\r\n    def __init__(self, x: Dict[P, Any]):\r\n        pass\r\n\r\nclass B(A):\r\n    def __init__(self, x: Dict[C, Any]):\r\n        super().__init__(x)\r\n```\r\n\r\nWhen running mypy on it, this warning appears:\r\n\r\n\u003e**Argument 1 to \"__init__\" of \"A\" has incompatible type \"Dict[C, Any]\"; expected \"Dict[P, Any]\"**\r\n\r\nWhy is this happening? If I do the same, but without using `Dict[]`, ie:\r\n```\r\nclass P:\r\n    pass\r\n\r\nclass C(P):\r\n    pass\r\n\r\nclass A:\r\n    def __init__(self, x: P):\r\n        pass\r\n\r\nclass B(A):\r\n    def __init__(self, x: C):\r\n        super().__init__(x)\r\n```\r\n\r\n I get no complains. I tried using `Mapping[]` instead of `Dict[]` but the same warning occurs. \r\n\r\nThis happens a lot in the code, as I am subclassing from a Library class, I cannot use cast every time, it's counter productive\r\n\r\n**Environment**\r\n\r\n- Mypy version used: 0.790\r\n- Python version used: 3.8.5\r\n- Operating system and version: Ubuntu 20.04\r\n\r\n\r\n","author":{"url":"https://github.com/VasLem","@type":"Person","name":"VasLem"},"datePublished":"2020-11-19T20:08:06.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/9738/mypy/issues/9738"}