Parameter expansion with ** rejected when calling aiohttp.web.Request.clone

[rra]

I'm getting a strange mypy error when calling aiohttp.web.Request.clone with a dict of parameters expanded with **. Is there some trick or missing feature to calling functions with ** expansion of parameters that I'm missing?

~ ❯ cat foo.py 
from aiohttp import web

def foo(request: web.Request) -> web.Request:
    overrides = {"remote": "1.1.1.1", "scheme": "https"}
    return request.clone(**overrides)
~ ❯ mypy foo.py 
foo.py:5: error: Argument 1 to "clone" of "Request" has incompatible type "**Dict[str, str]"; expected "Union[Mapping[Union[str, istr], str], CIMultiDict[str], CIMultiDictProxy[str]]"
Found 1 error in 1 file (checked 1 source file)

The relevant prototype is:

    def clone(self, *, method: str=sentinel, rel_url:
              StrOrURL=sentinel, headers: LooseHeaders=sentinel,
              scheme: str=sentinel, host: str=sentinel, remote:
              str=sentinel) -> 'Request':

It looks like the messy type is coming from LooseHeaders, and indeed str is not a valid type for LooseHeaders. Is that what mypy is complaining about? If so, is there a way to write this code that mypy will be happy with? (In my actual code, the overrides are dynamically determined.)

This is with Python 3.8.3rc1 and mypy 0.770, and aiohttp 3.6.2.

[JelleZijlstra]

You can do better with a TypedDict believe. Essentially the same issue was reported recently in #8772.