René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"typeshed annotations do not permit instantiation of urllib.error.HTTPError","articleBody":"Currently in typeshed, [urllib.error.HTTPError is (accurately) annotated](https://github.com/python/typeshed/blob/master/stdlib/3/urllib/error.pyi#L8) as inheriting both `URLError` and `urllib.response.addinfourl`. The `addinfourl` class inherits `addbase`, which [is annotated](https://github.com/python/typeshed/blob/master/stdlib/3/urllib/response.pyi#L6) as inheriting [typing.BinaryIO](https://github.com/python/typing/blob/master/src/typing.py#L2312). This appears to be an attempt to deal with the fact that `addbase` [actually inherits](https://github.com/python/cpython/blob/master/Lib/urllib/response.py#L14) the (private) `tempfile._TemporaryFileWrapper`, which is supposed to wrap a \"file-like object\", and [proxies all attribute access to the wrapped object](https://github.com/python/cpython/blob/master/Lib/tempfile.py#L473).\r\n\r\nThis makes some sense: `BinaryIO` is supposed to be the typing \"definition\" of what \"file-like object\" means (at least in binary mode). And this works OK for type-checking code that accesses \"file-like\" methods on an `HTTPError` instance. But it makes it impossible to actually instantiate an `HTTPError` without a spurious mypy error, because the methods of `typing.BinaryIO` (and its parent `typing.IO`) [are all decorated as @abstractmethod](https://github.com/python/typeshed/blob/master/stdlib/3/typing.pyi#L393), and most of them are not overridden by the typeshed annotation of `addbase` or `addinfourl`.\r\n\r\nSo if you type-check this code (which works fine at runtime):\r\n\r\n```\r\nfrom io import StringIO\r\nfrom urllib.error import HTTPError\r\n\r\nhttp_error = HTTPError(\"\", 500, \"message\", dict(), StringIO(''))\r\n```\r\n\r\nmypy gives you:\r\n\r\n```\r\nerror: Cannot instantiate abstract class 'HTTPError' with abstract attributes '__enter__', '__exit__', ... and 'writelines' (16 methods suppressed)\r\n```\r\n\r\nI'm filing an issue rather than going straight to pull request because the correct fix here isn't obvious to me, and I'm hoping someone with more typeshed experience can offer a preferred solution. If so, I'm happy to implement it. The obvious solution seems to be repeating all the method definitions from `typing.BinaryIO` and `typing.IO` in the typeshed annotation for `addbase`, without `@abstractmethod`, but I'm hoping there might be an option that avoids this duplication.","author":{"url":"https://github.com/carljm","@type":"Person","name":"carljm"},"datePublished":"2017-06-01T04:10:58.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/1377/typeshed/issues/1377"}