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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Incorrect redundant cast warning in lambda","articleBody":"With a `cast()` in a lambda, `--warn-redundant-cast` tells me to remove the cast, but then I get a different error if I actually do so. This is a regression in 0.790.\r\n\r\n```\r\n$ cat tmp/matchcast.py \r\nfrom typing import cast, Match, Pattern\r\n\r\n\r\ndef _get_nodes(key: str, rgx: Pattern[str]) -\u003e None:\r\n    matches = rgx.fullmatch(key)\r\n    if matches is None:\r\n        return\r\n\r\n    sorted(\r\n        matches.groupdict().items(),\r\n        key=lambda g: cast(Match[str], matches).start(g[0]),\r\n    )\r\n$ mypy --warn-redundant-casts tmp/matchcast.py \r\ntmp/matchcast.py:11: error: Redundant cast to \"Match[str]\"\r\nFound 1 error in 1 file (checked 1 source file)\r\n```\r\nAnd if I remove the cast:\r\n```\r\n$ mypy --warn-redundant-casts tmp/matchcast.py \r\ntmp/matchcast.py:11: error: Item \"None\" of \"Optional[Match[str]]\" has no attribute \"start\"\r\nFound 1 error in 1 file (checked 1 source file)\r\n```\r\n\r\n**Your Environment**\r\n\r\n- Mypy version used: 0.790\r\n- Mypy command-line flags: `--warn-redundant-casts`\r\n- Python version used: 3.6\r\n- Operating system and version: Ubuntu\r\n","author":{"url":"https://github.com/JelleZijlstra","@type":"Person","name":"JelleZijlstra"},"datePublished":"2020-10-09T18:43:15.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/9568/mypy/issues/9568"}