Switch to explicit typing.Optional throughout

[michaeloliverx]

See the following snippet:

from contextlib import AsyncExitStack

import httpx


async def main() -> None:
    async with AsyncExitStack() as stack:
        http_client = await stack.enter_async_context(httpx.AsyncClient())
        reveal_type(http_client)

Output with strict = false:

repro.py:9: note: Revealed type is "httpx._client.AsyncClient*"

Output with strict = true:

repro.py:8: error: Need type annotation for "http_client"  [var-annotated]
repro.py:8: error: Argument 1 to "enter_async_context" of "AsyncExitStack" has incompatible type "AsyncClient"; expected "AsyncContextManager[<nothing>]"  [arg-type]
repro.py:9: note: Revealed type is "Any"
Found 2 errors in 1 file (checked 1 source file)

---

I initially raised an issue at python/mypy#12226 but it looks to be an issue with httpx. They said

The annotations at

httpx/httpx/_client.py

Line 1970 in 7883c98

async def __aexit__(

need to be changed to Optional.

[florimondmanca]

Hi @michaeloliverx,

Yup, this seems correct and well scoped, I guess at this point a PR attempting to fix that type annotation to Optional and see if it resolves this item would be on point.

[tomchristie]

Perhaps we should re-title this as the more general case.

Something like "Switch to explicit typing.Optional throughout" (?)

[tomchristie]

See also #1760, #1747

[nhoad]

If no one has picked this up yet, I'm happy to take a crack at it.

I've been working on it a little bit and I've got the total number of errors from mypy --strict httpx down from 437 to 207, just by adding typing.Optional or adding None to some already existing typing.Union definitions (e.g. httpx._types.HeaderTypes).

Happy to continue the work and open a PR if people are interested.

[florimondmanca]

@nhoad Hi, FYI it looks like there's initial work on this here: #2096