redis/redis-py · error · TypeError

Async Redis client does not support class assignment

Error message

Async Redis client does not support class assignment

What it means

Raised by AsyncBasicKeyCommands.__setitem__ when you assign async_client[key] = value. The sync client maps this to SET, but the async SET must be awaited and cannot run inside the synchronous __setitem__ dunder, so assignment via subscript is disabled.

Source

Thrown at redis/commands/core.py:4818

        if minmatchlen is not None and minmatchlen != 0:
            pieces.extend(["MINMATCHLEN", minmatchlen])
        if withmatchlen:
            pieces.append("WITHMATCHLEN")
        return self.execute_command("LCS", *pieces, keys=[key1, key2])


class AsyncBasicKeyCommands(BasicKeyCommands):
    def __delitem__(self, name: KeyT):
        raise TypeError("Async Redis client does not support class deletion")

    def __contains__(self, name: KeyT):
        raise TypeError("Async Redis client does not support class inclusion")

    def __getitem__(self, name: KeyT):
        raise TypeError("Async Redis client does not support class retrieval")

    def __setitem__(self, name: KeyT, value: EncodableT):
        raise TypeError("Async Redis client does not support class assignment")

    async def watch(self, *names: KeyT) -> None:
        return super().watch(*names)

    async def unwatch(self) -> None:
        return super().unwatch()


class ListCommands(CommandsProtocol):
    """
    Redis commands for List data type.
    see: https://redis.io/topics/data-types#lists
    """

    @overload
    def blpop(
        self: SyncClientProtocol, keys: KeysT, timeout: Number | None = 0
    ) -> BlockingListPopResponse: ...

View on GitHub (pinned to da03cdc7e8)

Solutions

Replace async_client[key] = value with await async_client.set(key, value).
Use the explicit set command for all async writes.

Example fix

# before
r['mykey'] = 'v'
# after
await r.set('mykey', 'v')

Defensive patterns

Strategy: type-guard

Type guard

import redis.asyncio as aioredis
def is_async_client(client) -> bool:
    return isinstance(client, aioredis.Redis)

Prevention

Replace r[key] = value with await r.set(key, value) in async code.
Grep for r[' = assignment patterns when porting to async.
Use the explicit set() command for writes.

When it happens

Trigger: Writing `async_client['mykey'] = 'v'` against an instance of redis.asyncio.Redis.

Common situations: Porting sync dict-style writes to async; copy-pasting sync examples that use r[key] = value.

Related errors

AI-assisted analysis of redis/redis-py@da03cdc7e8 (2026-08-04). Data as JSON: /data/errors/a41bfede1e4e4ae7.json. Report an issue: GitHub.