pyncette

Overview

A reliable distributed scheduler with pluggable storage backends for Async Python.

• Free software: MIT license

Installation

Minimal installation (just SQLite persistence):

pip install pyncette

Full installation (all the backends and Prometheus metrics exporter):

pip install pyncette[all]

You can also install the in-development version with:

pip install https://github.com/tibordp/pyncette/archive/master.zip

Documentation

https://tibordp.github.io/pyncette/

Usage example

Simple in-memory scheduler (does not persist state)

from pyncette import Pyncette, Context

app = Pyncette()


@app.task(schedule="* * * * *")
async def foo(context: Context):
    print("This will run every minute")


if __name__ == "__main__":
    app.main()

Persistent distributed cron using Redis (coordinates execution with parallel instances and survives restarts)

from pyncette import Pyncette, Context
from pyncette.redis import redis_repository

app = Pyncette(repository_factory=redis_repository, redis_url="redis://localhost")


@app.task(schedule="* * * * * */10")
async def foo(context: Context):
    print("This will run every 10 seconds")


if __name__ == "__main__":
    app.main()

See the examples directory for more examples of usage.

Use cases

Pyncette is designed for reliable (at-least-once or at-most-once) execution of recurring tasks (think cronjobs) whose lifecycles are managed dynamically, but can work effectively for non-reccuring tasks too.

Example use cases:

• You want to perform a database backup every day at noon
• You want a report to be generated daily for your 10M users at the time of their choosing
• You want currency conversion rates to be refreshed every 10 seconds
• You want to allow your users to schedule non-recurring emails to be sent at an arbitrary time in the future

Pyncette might not be a good fit if:

• You want your tasks to be scheduled to run (ideally) once as soon as possible. It is doable, but you will be better served by a general purpose reliable queue like RabbitMQ or Amazon SQS.
• You need tasks to execute at sub-second intervals with low jitter. Pyncette coordinates execution on a per task-instance basis and this corrdination can add overhead and jitter.

Supported backends

Pyncette comes with an implementation for the following backends (used for persistence and coordination) out-of-the-box:

• SQLite (included)
• Redis (pip install pyncette[redis])
• PostgreSQL (pip install pyncette[postgres])
• MySQL 8.0+ (pip install pyncette[mysql])
• MongoDB (pip install pyncette[mongodb])
• Amazon DynamoDB (pip install pyncette[dynamodb])

Pyncette imposes few requirements on the underlying datastores, so it can be extended to support other databases or custom storage formats / integrations with existing systems. For best results, the backend needs to provide:

• Some sort of serialization mechanism, e.g. traditional transactions, atomic stored procedures or compare-and-swap
• Efficient range queries over a secondary index, which can be eventually consistent

Development

Prerequisites

Install uv for fast package management:

curl -LsSf https://astral.sh/uv/install.sh | sh

Setup Development Environment

Sync dependencies and install the package in editable mode:

uv sync --extra all

Running Tests

Unit tests (fast, no external dependencies):

uv run pytest -m "not integration" tests

Integration tests (requires Redis, PostgreSQL, MySQL, MongoDB, DynamoDB):

Using Docker Compose to set up all backends:

docker-compose up -d
docker-compose run --rm shell
uv run pytest tests

Or manually with services running locally:

uv run pytest tests

Test on specific Python version:

uv venv --python 3.11
uv sync --extra all
uv run pytest tests

Code Quality

Run linting and type checking:

uv run pre-commit run --all-files
uv run ty check src examples

Building Documentation

uv run mkdocs build
# Or serve locally with live reload
uv run mkdocs serve

Building the Package

uv build