Duron

Duron runs durable async Python workflows. A workflow coordinates work through Duron's context; effects perform external I/O and other nondeterministic work. Duron records operations and their outcomes so a workflow can replay them after a restart and continue unfinished work.

Requires Python 3.11 or later. Tested on CPython 3.11 through 3.15.

uv pip install duron

Run a workflow

import asyncio

import duron


@duron.effect
async def greet(_ctx: duron.EffectContext, name: str) -> str:
    print(f"greeting {name}")
    await asyncio.sleep(0.1)
    return f"Hello, {name}!"


@duron.workflow
async def hello(ctx: duron.WorkflowContext, name: str) -> str:
    return await ctx.call(greet, name)


async def main() -> None:
    async with duron.SQLiteScheduler("duron.db", workflows=[hello]) as scheduler:
        run = await scheduler.submit(hello, "hello-alice", "Alice")
        print(await run.result())


asyncio.run(main())

Run this example again with the same database to read the recorded greeting without calling the effect again. The run ID, "hello-alice", identifies one invocation: submitting the same workflow and arguments with that ID returns the existing run.

Restart and recover

Register workflow implementations with workflows=[hello] so the scheduler can recover unfinished runs when it opens the database. You do not need to submit those runs again.

SQLiteScheduler owns its database file exclusively. Use one active scheduler per file; close it before another process opens the same database. After a crash, a new scheduler can recover immediately.

Completed effects replay their recorded outcomes. If an effect's outcome was not recorded before a failure, Duron blocks the run rather than invoking it again. Use application operation IDs to reconcile uncertain external changes such as payments before starting a new run.

Interact with running workflows

Typed input and output ports let applications interact with workflows and effects. Output ports support async for and resumable readers. See the getting started guide and documentation for details.

Develop locally

From a repository checkout:

uv sync
uv run pytest
uv run ruff check
uv run ruff format --check
uv run pyright --verifytypes duron --ignoreexternal
uv run --group docs zensical build

Preview the documentation with uv run --group docs zensical serve.