philiprehberger-once 0.1.5

Ensure a function runs only once, regardless of how many times it's called

philiprehberger-once

Ensure a function runs only once, regardless of how many times it's called.

Install

pip install philiprehberger-once

Usage

from philiprehberger_once import once

@once
def load_config():
    print("Loading...")
    return {"debug": True}

load_config()  # prints "Loading...", returns {"debug": True}
load_config()  # returns {"debug": True} without printing

Async support

import asyncio
from philiprehberger_once import once

@once
async def fetch_token():
    print("Fetching...")
    return "abc-123"

asyncio.run(fetch_token())  # prints "Fetching...", returns "abc-123"
asyncio.run(fetch_token())  # returns "abc-123" without fetching

Once per key

from philiprehberger_once import once_per_key

@once_per_key
def connect(host, port=5432):
    print(f"Connecting to {host}...")
    return f"conn:{host}"

connect("db-1")  # prints "Connecting to db-1...", returns "conn:db-1"
connect("db-1")  # returns cached "conn:db-1"
connect("db-2")  # prints "Connecting to db-2...", returns "conn:db-2"

Reset and inspect

from philiprehberger_once import once

@once
def init():
    return 42

init()
init.called   # True
init.reset()
init.called   # False
init()        # runs again

API

Function / Property	Description
once(fn)	Decorator. Runs fn once, caches and returns the result on subsequent calls. Thread-safe. Supports async.
once_per_key(fn)	Decorator. Runs fn once per unique first argument. Thread-safe.
.called	bool for once, dict[key, bool] for once_per_key. Whether the function has been called.
.reset()	Clear cached result so the function can run again. once_per_key accepts an optional key argument.

Development

pip install -e .
python -m pytest tests/ -v

License

MIT