Various improvements for the mailbox stubs #14950
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* Use `_typeshed.SupportsItems` instead of custom `_HasItems` protocol. * Use a custom covariant protocol for mailbox messages. * Add `Mailbox._dump_message`. * Return a protocol from abstract method `Mailbox.get_file()`. * Return concrete type `BytesIO` instead of `typing.IO` from `Babyl.get_file()`. * Use our custom protocol instead of semi-protocol `typing.IO` in the remaining cases. Closes: python#14935
srittau commented Oct 30, 2025
stdlib/mailbox.pyi Outdated
| class Mailbox(Generic[_MessageT]): | ||
| # Common interface for get_file() return types. | ||
| @type_check_only | ||
| class _GetFileReturn(Protocol[_AnyStr]): |
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This protocol is only generic, because _ProxyFile (and _PartialFile) are unnecessarily generic at runtime.
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Since this was changed upstream, I removed the generic marker here and for _ProxyFile, even if the latter was technically generic up until Python 3.14.
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| According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉 |
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_typeshed.SupportsItemsinstead of custom_HasItemsprotocol.Mailbox._dump_message.Mailbox.get_file().BytesIOinstead oftyping.IOfromBabyl.get_file().typing.IOin the remaining cases.Closes: #14935