René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"tempfile issues","articleBody":"I would expect the following to work:\r\n\r\n```python\r\nfrom tempfile import TemporaryFile\r\nfrom typing import BinaryIO\r\n\r\n\r\ndef make_temp() -\u003e BinaryIO:\r\n    return TemporaryFile()\r\n```\r\n\r\nBut mypy 0.540 on Python 3.6 complains:\r\n\r\n```\r\nfoo.py:6: error: Incompatible return value type (got \"IO[Any]\", expected \"BinaryIO\")\r\n```\r\n\r\nI am not sure where exactly the problem is. `TemporaryFile` returns `IO[Any]`. According to https://docs.python.org/3/library/typing.html `BinaryIO` is just an alias for `IO[bytes]`, in which case the above should work, like the following code does:\r\n\r\n```python\r\nfrom tempfile import TemporaryFile\r\nfrom typing import IO\r\n\r\n\r\nMyBinaryIO = IO[bytes]\r\n\r\n\r\ndef make_temp() -\u003e MyBinaryIO:\r\n    return TemporaryFile()\r\n```\r\n\r\nBut actually, typing from Python 3.6 derives `BinaryIO` from `IO[bytes]` and adds methods `write()` and `__enter__()`.\r\n\r\nIs this a an issue with the typing implementation of `BinaryIO` or with the documentation? In the latter case, should the return types of `TemporaryFile` et al. be changed to `Union[BinaryIO, StringIO]`?\r\n","author":{"url":"https://github.com/srittau","@type":"Person","name":"srittau"},"datePublished":"2017-12-11T19:07:49.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/1780/typeshed/issues/1780"}