René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Argument Clinic: DSLParser.parse_converter() can return an incorrect kwargs dict","articleBody":"_Originally posted by @AlexWaygood in https://github.com/python/cpython/issues/106354#issuecomment-1617797726_:\r\n\r\n```\r\nTools/clinic/clinic.py:5039: error: Incompatible return value type (got\r\n\"tuple[str, bool, dict[str | None, Any]]\", expected\r\n\"tuple[str, bool, dict[str, Any]]\")  [return-value]\r\n                    return name, False, kwargs\r\n                           ^~~~~~~~~~~~~~~~~~~\r\n```\r\n\r\nI think mypy is flagging a real bug in the code here. The issue is this block of code here:\r\n\r\nhttps://github.com/python/cpython/blob/d694f043ae25308dda607fad4ea1d8d85d79982f/Tools/clinic/clinic.py#L5033-L5039\r\n\r\nThe function is annotated as return `tuple[str, bool, KwargDict]`, and `KwargDict` is a type alias for `dict[str, Any]`. It's important that the dictionary that's the third element of the tuple only has strings as keys. If it doesn't, then this will fail:\r\n\r\nhttps://github.com/python/cpython/blob/d694f043ae25308dda607fad4ea1d8d85d79982f/Tools/clinic/clinic.py#L4617\r\n\r\nThe code as written, however, doesn't guarantee that all the keys in the `kwargs` dictionary will be strings. In the dictionary comprehension, we can see that `annotation` is an `ast.Call` instance. That means that `annotation.keywords` is of type `list[ast.keyword]` -- we can see this from typeshed's stubs for the `ast` module (which are an invaluable reference if you're working with ASTs in Python!): https://github.com/python/typeshed/blob/18d45d62aabe68fce78965c4920cbdeddb4b54db/stdlib/_ast.pyi#L324-L329. If `annotation.keywords` is of type `list[ast.keyword]`, that means that the `node` variable in the dictionary comprehension is of type `keyword`, which means (again using typeshed's `ast` stubs), that `node.arg` is of type `str | None`: https://github.com/python/typeshed/blob/18d45d62aabe68fce78965c4920cbdeddb4b54db/stdlib/_ast.pyi#L516-L520. AKA, the keys in this dictionary are not always guaranteed to be strings -- there's a latent bug in this code!\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-106361\n* gh-106364\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/erlend-aasland","@type":"Person","name":"erlend-aasland"},"datePublished":"2023-07-03T11:11:32.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":10},"url":"https://github.com/106359/cpython/issues/106359"}