Use AnyStr where appropriate

[lovelydinosaur]

Refs #993, #985

Makes more careful use of typing.Union[str, bytes] vs. typing.AnyStr.

Use AnyStr where we'd expect the types to be the same across everything in the signature. Eg. typing.Mapping[AnyStr, AnyStr] means "choose either str or bytes here, but be consistent.".

Resolves an issues where mypy errors with a really simple bit of httpx usage...

example.py

importhttpxheaders= {"content-type": "example"}
httpx.Headers(headers)

MyPy

$ venv/bin/mypy example.py example.py:5: error: Argument 1 to "Headers" has incompatible type"Dict[str, str]"; expected "Union[Headers, Dict[Union[str, bytes], Union[str, bytes]], Sequence[Tuple[Union[str, bytes], Union[str, bytes]]], None]"
Found 1 error in 1 file (checked 1 source file)

[lovelydinosaur]

After this change...

$ venv/bin/mypy example.py Success: no issues found in 1 source file

[yeraydiazdiaz]

Eg. typing.Mapping[AnyStr, AnyStr] means "choose either str or bytes here, but be consistent.".

I don't think that's the case, either using Mapping or Dict, mypy is fine with the code below:

importtypingAnyStrDict=typing.Dict[typing.AnyStr, typing.AnyStr]
AnyStrMapping=typing.Mapping[typing.AnyStr, typing.AnyStr]
d: AnyStrDict= {b"foo": "bar"}
m: AnyStrMapping= {b"foo": "bar"}

[lovelydinosaur]

Gotcha. It’s at least “consistent within this part of the type” tho right? Eg. Keys as str or Keys as bytes, not keys as str or bytes.

[yeraydiazdiaz]

Apparently not 😕 , again mypy is completely fine with the code below:

importtypingAnyStrDict=typing.Dict[typing.AnyStr, typing.AnyStr]
AnyStrMapping=typing.Mapping[typing.AnyStr, typing.AnyStr]
d: AnyStrDict= {"foo": "bar", b"bar": "baz"}
m: AnyStrMapping= {b"foo": "bar", "foo": "baz"}

Looks like the guarantees only hold in the context of a function. From the docs:

It is meant to be used for functions that may accept any kind of string without allowing different kinds of strings to mix.

[lovelydinosaur]

Interestingly MyPy's behaviour varies depending on if the annotation is used directly or indirectly, eg...

fromtypingimportUnion, Dict, Sequence, Tuple, AnyStrHeaderTypes=Union[
Dict[AnyStr, AnyStr], Sequence[Tuple[AnyStr, AnyStr]],
]
deffoo(h: HeaderTypes) ->None:
print(h)
defbar(h: Union[Dict[AnyStr, AnyStr], Sequence[Tuple[AnyStr, AnyStr]]]) ->None:
print(h)
headers= {b"content-type": b"example", "accept": "*/*"}
foo(headers) # Okbar(headers) # Error 

[florimondmanca]

LGTM!