idempot 0.1.0

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idempot

Idempotency for APIs via decorators. Framework-agnostic core with adapters for FastAPI and Flask.

Install

pip install idempot                  # core + backends (pyyaml, redis)
pip install "idempot[fastapi]"       # core + fastapi
pip install "idempot[flask]"         # core + flask
pip install "idempot[dev]"           # everything + test/lint deps

Zero-config Quickstart

No config needed. Import, decorate, done.

FastAPI

# app.py
from fastapi import FastAPI, Request
from idempot.contrib.fastapi import idempotent

app = FastAPI()

@app.post("/charge")
@idempotent
async def charge(request: Request):
    body = await request.json()
    return {"charged": body["amount"]}

uvicorn app:app --reload

Flask

# app.py
import flask
from idempot.contrib.flask import idempotent

app = flask.Flask(__name__)

@app.post("/charge")
@idempotent
def charge():
    data = flask.request.get_json()
    return flask.jsonify({"charged": data["amount"]})

flask --app app run

Defaults: memory backend, 24h TTL, Idempotency-Key header, 5s lock timeout.

Client Usage

Send Idempotency-Key header with every request:

curl -X POST http://localhost:8000/charge \
  -H "Idempotency-Key: abc-123" \
  -H "Content-Type: application/json" \
  -d '{"amount": 99}'
# → {"charged": 99}

# Same key → replayed response (handler not called)
curl -X POST http://localhost:8000/charge \
  -H "Idempotency-Key: abc-123" \
  -H "Content-Type: application/json" \
  -d '{"amount": 50}'        # different body, ignored
# → {"charged": 99}           # same reply

Configuration

Option A — configure() at startup

In your app entry point, before registering routes:

from idempot import configure

# Redis in production:
configure(
    backend="redis",
    redis_url="redis://localhost:6379",
    redis_key_prefix="myapp:",
    default_ttl=86400,
    header_name="Idempotency-Key",
    lock_timeout=5,
    cache_on_status=[200, 201],
)

# Or override just one thing:
configure(backend="memory", default_ttl=3600)

Option B — YAML file

Create idempot-config.yaml in your project root:

backend: redis
redis:
  url: redis://localhost:6379
  key_prefix: "myapp:"
default_ttl: 86400
header_name: Idempotency-Key
lock_timeout: 5
cache_on_status: [200, 201]

from idempot import configure
configure(config_path="idempot-config.yaml")

A working example file: idempot-config.example.yaml

The config file is not auto-generated. If no config file is found and configure() is never called, memory backend + defaults are used.

Config reference

Key	Default	Description
backend	memory	memory or redis
redis.url	redis://localhost:6379	Redis connection URL
redis.key_prefix	idempot:	Prefix for Redis keys
default_ttl	86400 (24h)	Seconds before cached response expires
header_name	Idempotency-Key	HTTP header to read the key from
lock_timeout	5	Max seconds to wait for concurrent same-key request
cache_on_status	[200]	Which HTTP status codes get cached
max_body_size	10485760 (10 MB)	Largest response body to cache

Per-endpoint Overrides

@app.post("/payments")
@idempotent(
    ttl=3600,                      # cache 1 hour (instead of default 24h)
    required=True,                 # reject requests without key → 400
    cache_on_status=[200, 201],    # cache on 200 or 201
    lock_timeout=10,               # wait up to 10s for concurrent
)
async def process_payment(request: Request):
    ...

Override params: ttl, required, lock_timeout, cache_on_status, max_body_size.

Import Cheatsheet

Context	Import
Config & setup	from idempot import configure, get_config
FastAPI decorator	from idempot.contrib.fastapi import idempotent
Flask decorator	from idempot.contrib.flask import idempotent
Base decorator (no framework)	from idempot import idempotent
Exceptions	from idempot import IdempotencyKeyMissingError, KeyConflictError
Backends (custom)	from idempot.backends.memory import MemoryBackend

How It Works

1. Decorator reads Idempotency-Key from request headers
2. Key missing → 400 if required=True, otherwise handler runs normally (not cached)
3. Key in cache → replays stored response verbatim (same status, headers, body)
4. Key new → acquires distributed lock (Redis SETNX) → runs handler → caches response → releases lock
5. Concurrent same-key → second request polls for cached response, returns it. If first request exceeds lock_timeout → 409 Conflict

Backends

• Memory (default, dev): dict-backed, no persistence
• Redis (prod): SETNX locks, SETEX caching with TTL, key prefix isolation

License

MIT