Improve typing

[karpetrosyan]

Should we replace Dict[str, any] with typing.TypedDict as an Extensions type?

Now:

Extensions = Mapping[str, Any]

That means any dictionary with the key type of str can be passed, and the type checker will recognize it as a valid dictionary.

import httpcore
httpcore.Request(..., extensions={'not_exists': type}) # valid

Usage of TypeDict

import typing

class Extensions(typing.TypedDict):
    timeout: int

invalid_req: Extensions = {'timeout': type} # invalid (type)
valid_req: Extensions = {'timeout': 1} # valid
invalid_req: Extensions = {'t': 1} # invalid (missing timeout)

It's a good UX improvement, in my opinion.

[tomchristie]

That's an interesting suggestion, and you're not the first to make it.

I'm not sure about it because...

The extensions that are valid depend on the transport that's in use. Using the dict typing here implies (or is implied by) that loose coupling.