Merge stdlib/{2,3}/os/path.pyi #1150
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To be renamed into stdlib/2and3/os/path.pyi later. Also fixes python#50
stdlib/2/os/path.pyi
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| if sys.version_info >= (3, 5): | ||
| def commonpath(paths: Sequence[AnyStr]) -> AnyStr: ... | ||
| if sys.version_info >= (3,): | ||
| # NOTE: Empty List[bytes] results in '' (str) => fall back to Any return type. |
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We could handle this with an overload instead.
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Is there a way to describe the type of an empty list?
stdlib/2/os/path.pyi
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| # NOTE: Empty List[bytes] results in '' (str) => fall back to Any return type. | ||
| def commonprefix(list: List[AnyStr]) -> Any: ... | ||
| else: | ||
| def commonprefix(list: List[AnyStr]) -> AnyStr: ... |
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Mixed lists actually work fine:
In [4]: os.path.commonprefix([u'hello', b'hello'])
Out[4]: u'hello'
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Looking at the python2 version (because python3 does not let you mix types) it looks like the return type is the type of the min element of the list, https://github.com/python/cpython/blob/2.7/Lib/genericpath.py#L76
So maybe I can do an overload like this:
@overload
def commonprefix(list: List[AnyStr]) -> AnyStr: ...
@overload
def commonprefix(list: List[Union[bytes], Union[Text]]) -> Union[bytes, Text]
But then you have the dreaded Union in a return value.
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Do you mean List[Union[bytes, Text]] in the second overload?
I think we can just do def commonprefix(list: Sequence[Union[bytes, Text]]) -> Any: ... (not a List so we don't get hit by invariance).
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Ah I didn't want to use Sequence[Union[bytes, Text]] because in python3 it's not supported.
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| _T = TypeVar('_T') | ||
| _PathType = Union[bytes, Text] |
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Looked into this I think it need more work. PathLike is 3.6 only and I imagine some methods support it. But I'm not sure this is the change to work on that.
| def commonpath(paths: Sequence[AnyStr]) -> AnyStr: ... | ||
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| # NOTE: Empty lists results in '' (str) regardless of contained type. | ||
| # Also, in Python 2 mixed sequences of Text and bytes results in either Text or bytes |
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This type signature won't allow mixed lists, right? A Sequence[Union[bytes, Text]] is not a Sequence[AnyStr].
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Sequence[AnyStr] works in python 2 because str gets promoted to Text
And sadly I can't overload where the argument varies by what's inside the Sequence.
Basically if I do in Python 2:
@overload
def commonprefix(list: Sequence[str]) -> str: ...
@overload
def commonprefix(list: Sequence[Text]) -> Any: ...
I get this error:
error: Overloaded function signatures 1 and 2 overlap with incompatible return types
It doesn't work with List[X] or with Sequence[bytes] in python 3. I even tried introducing a _Str = TypeVar("_Str", str) and separating using that, but that doesn't work either.
So I opted for the most generic thing.
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Oh right, I forgot about that promotion. Seems like this is the best we can do then. Thanks for explaining!
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Thanks! |
To be renamed into stdlib/2and3/os/path.pyi later.
Also fixes #50