Redis asyncio invalid type definition.

[s3rius]

I found a problem using types-redis library with new redis.asyncio module.

The problem is that mypy throws an error.

The code:

async def get_redis_connection(request: Request) -> AsyncGenerator[Redis, None]:

The error:

testotlp/services/redis/dependency.py:7: error: Missing type parameters for generic type "Redis"  [type-arg]
    async def get_redis_connection(request: Request) -> AsyncGenerator[Redis, None]:

I tried to fix it by providing an Any generic type.

But found another issue. Mypy detects no error for the following code:

async def get_redis_connection(request: Request) -> AsyncGenerator[Redis[Any], None]:

But I cant start my program because of this:

  File "/testmypy/services/redis/dependency.py", line 7, in <module>
    async def get_redis_connection(request: Request) -> AsyncGenerator[Redis[Any], None]:
  File "../lib/python3.9/typing.py", line 277, in inner
    return func(*args, **kwds)
  File "../lib/python3.9/typing.py", line 1003, in __class_getitem__
    _check_generic(cls, params, len(cls.__parameters__))
  File "../lib/python3.9/site-packages/typing_extensions.py", line 92, in _check_generic
    raise TypeError(f"{cls} is not a generic class")
TypeError: <class 'redis.asyncio.client.Redis'> is not a generic class

I guess it's a problem.

[s3rius]

Answered here: #7597 (comment)

[s3rius]

I think this issue must be reopened, because FastAPI depends on type system and the redis-types lib can't be used with FastAPI.

For all folks, who use redis with FastAPI consider downgrading types-redis to 4.2.0, delete .mypy_cache and rerun all checks.
This version of types-redis haven't got type annotations for asyncio package, but mypy won't throw any error.

Or you can downgrade mypy to 0.910, it also doesn't give this error.

[JelleZijlstra]

The runtime TypeError can be worked around by quoting the annotation, either explicitly (AsyncGenerator["Redis[Any]", None]) or with from __future__ import annotations.

Is there any other remaining problem?

[s3rius]

Yes. The problem is that FastAPI framework uses types to inject dependencies. Quoting "Redis[Any]" doesn't work.
Importing from __future__ import annotations also doesn't work.

Here is a minimum reproducible example:

from __future__ import annotations

from typing import Any, AsyncGenerator

from fastapi import Depends, FastAPI, Request
from redis.asyncio import ConnectionPool, Redis

pool = ConnectionPool.from_url("redis://localhost:6379/0")


async def get_redis_connection(request: Request) -> AsyncGenerator[Redis[Any], None]:
    redis_client: Redis[Any] = Redis(connection_pool=request.app.state.redis_pool)

    try:  # noqa: WPS501
        yield redis_client
    finally:
        await redis_client.close()


app = FastAPI()


@app.get("/")
async def handler(redis: Redis[Any] = Depends(get_redis_connection)) -> None:
    await redis.set("key", "val")

Dependencies:

fastapi==0.78.0
redis==4.3.4
types-redis==4.3.3

Mypy config from pyproject.toml:

[tool.mypy]
strict = true
ignore_missing_imports = true
allow_subclassing_any = true
allow_untyped_calls = true
pretty = true
show_error_codes = true
implicit_reexport = true
allow_untyped_decorators = true
warn_unused_ignores = false
warn_return_any = false
namespace_packages = true

If you run this file you'll get an error.

[srittau]

In this particular case, fastapi doesn't seem to use the type stubs for runtime type checking, instead using the runtime classes. I'm not sure that is even easily possible. That said, this is a larger issue that needs to be discussed on typing-sig, but unfortunately it's out of scope to fix in typeshed.

[s3rius]

But maybe, if I provide a request with Redis type without Generic in definition, it will work as expected. Or it would be incorrect?

[srittau]

That should help and is the correct long-term solution anyway, as redis is moving towards including types themselves.

[s3rius]

Ok. I'll keep this issue open to be able to link pull request to it.

Can you assign this issue to me?

[samuelcolvin]

There's another problem here - inheriting from Redis.

Clearly we can't do class ArqRedis('Redis[bytes]'):, but class ArqRedis(Redis): is giving a typing error.

Frankly, I think that having the Redis stub as generic and the runtime class as not generic is a mistake.

[JelleZijlstra]

You can work around this with something like:

if TYPE_CHECKING:
    _RedisBase = Redis[bytes]
else:
    _RedisBase = Redis

class ArgRedis(_RedisBase): ...

Admittedly it's not pretty.

[hauntsaninja]

Relevant section of mypy docs:

https://mypy.readthedocs.io/en/latest/runtime_troubles.html#using-classes-that-are-generic-in-stubs-but-not-at-runtime

[samuelcolvin]

Thanks both, that's what I have python-arq/arq#331.