Pyright reports false positive error with async streams

[RobertCraigie]

Problem

from httpx import AsyncClient

async def main(url: str) -> None:
    client = AsyncClient()

    async with client.stream('GET', url) as resp:
        ...

Pyright reports:

error: Object of type "AsyncIterator[Response]" cannot be used with "with" because it does not implement __aenter__ (reportGeneralTypeIssues)

Solution

Although I haven't checked, I am fairly certain that this issue can be solved by changing how httpx/_compat.py imports the async context manager:

import sys

# `contextlib.asynccontextmanager` exists from Python 3.7 onwards.
# For 3.6 we require the `async_generator` package for a backported version.
if sys.version_info >= (3, 7):
    from contextlib import asynccontextmanager
else:
    from async_generator import asynccontextmanager

[tomchristie]

I am fairly certain that this issue can be solved by changing how httpx/_compat.py imports the async context manager

Okay, I'm curious... why might that satisfy pyright's type checking, where the try... except ImportError ... style would not?

# `contextlib.asynccontextmanager` exists from Python 3.7 onwards.
# For 3.6 we require the `async_generator` package for a backported version.
try:
    from contextlib import asynccontextmanager  # type: ignore
except ImportError:
    from async_generator import asynccontextmanager  # type: ignore # noqa

If you're able to verify that assumption then I guess we could consider if it's worth switch our style for conditional imports.

[tomchristie]

Because pyright is static type checking tool that does not run Python code in order to catch that ImportError

Okay. Does it recognise sys.version_info branching, then?

[HarrySky]

Yes, if you write it as if sys.version_info < (3, 8).

AFAIK it will not work if you use from sys import version_info

[tomchristie]

Okeydokes - I'd be happy to accept a pull request tweaking the conditional import there, then.

[HarrySky]

@RobertCraigie want to send a PR fixing your issue?

[RobertCraigie]

@RobertCraigie want to send a PR fixing your issue?

Yes, I'll send a PR as soon as possible.