Upgrade Redis stubs to 4.2.x

[Ankhas]

The redis-py package has been updated to 4.2.2 : https://github.com/redis/redis-py/releases/tag/v4.2.2 and currently stubs are in version 4.1.*

[kovalevvlad]

A big change here and the reason why I upvoted is the addition of asyncio

[AlexWaygood]

Thanks — PR welcome!

[srittau]

#7675 didn't add async support. Reopening.

[squaresmile]

Thank you for the updated redis typing. 2 things I noticed with the new types:

from redis.asyncio import Redis 

async def func(redis: Redis, redis_key: str): # 1
    return await redis.get(redis_key)         # 2

• 1 leads to mypy error Missing type parameters for generic type while TypeError: <class 'redis.asyncio.client.Redis'> is not a generic class.
• 2 leads to Incompatible types in "await" (actual type "Optional[Any]", expected type "Awaitable[Any]").

[srittau]

(1) is a general problem with types that are generic for type checking purposes, but not at runtime. Use:

async def func(redis: "Redis[Any]", redis_key: str):  # or even better Redis[str] or Redis[bytes]

Alternatively, if you want to leave out the quotes, use from __future__ import annotations.

python/typing#307 would also help with that.

(2) I think we will need to override all Redis commands in the corresponding classes accordingly. This is quite a big task, but all PRs are welcome.