kasper-idempotent 0.1.0

Idempotency-key decorator for exactly-once handlers, backed by Redis or in-memory.

kasper-idempotent

Decorate a handler with an idempotency key. Duplicate calls (retries, at-least-once queues) return the stored result instead of running again.

pip install kasper-idempotent          # in-memory store
pip install "kasper-idempotent[redis]" # + Redis store (multi-process)

from kasper_idempotent import idempotent, RedisStore

store = RedisStore("redis://localhost:6379")

@idempotent(store=store, key=lambda evt: evt["id"], ttl=3600)
def handle(evt):
    charge_card(evt)      # runs once per evt["id"], even on retries
    return {"ok": True}

How it works

On call it atomically claims the key (SET key ... NX):

• claim wins -> run the handler, store the result, return it.
• already done -> return the cached result (no re-run).
• in progress -> raise InProgress (a concurrent duplicate is still running).

The atomic claim is what prevents two simultaneous duplicates from both executing. Sync and async handlers are both supported.

MIT licensed.