aiolifecycle 0.1.8

Micro-framework to effectively run asyncio functions in synchronous contexts

aiolifecycle

Safely use asyncio handlers in synchronous context.

Use case

If you want to run an asyncio-based program in a synchronous context - such as a command line invocation - you can use asyncio.run from the standard library. But it immediately spins up and terminates an event loop. What if you want to a continuous workflow, where you can initialise and re-use resources?

The original need for this project arose when adapting an asyncio-based system to AWS Lambda, which makes multiple synchronous function calls in the same interpreter environment.

Installation

Run pip install aiolifecycle, or add it to your package dependencies.

Usage

Handler

Define your handler as an async function, and add the sync annotation. Then it can safely be called synchronously. An event loop will automatically be initialised with its associated resources.

import asyncio

from aiolifecycle import sync


@sync()
async def my_handler() -> None:
    await asyncio.sleep(1)

By default, handlers are eager, meaning an event loop will be created and initialisation functions will be immediately run on module import.

If you want to initialise resources only when a handler is first called, do:

import asyncio

from aiolifecycle import sync


@sync(eager=False)
async def my_handler() -> None:
    await asyncio.sleep(1)

Initialisation

You can define async initialisation functions to prepare resources for use by handlers. These can be simple async defs returning nothing.

In the following example, my_init will be called exactly once, before any handlers run.

import asyncio

from aiolifecycle import sync, init


@init
async def my_init() -> None:
    print('Hello, world!')


@sync
async def my_handler() -> None:
    await asyncio.sleep(1)

Initialisation order can be controlled with the order parameter. In the following example, hello will be called before world. Functions with the same order (or undefined order) are called in the order they were defined.

import asyncio

from aiolifecycle import sync, init

@init(order=20)
async def world() -> None:
    print('World!')


@init(order=10)
async def hello() -> None:
    print('Hello!')


@sync()
async def my_handler() -> None:
    await asyncio.sleep(1)

Initialisation functions can manage resources. You can simply return the resource from an init function (if no finalisation is necessary), or define it as an asynccontextmanager

Or you can use AsyncContextManagers, and access the resources they create by refering to the handler function. Proper lifetime will be managed internally, such that the initialisation will happen once.

import json
from contextlib import asynccontextmanager
from typing import AsyncIterator

import aiofiles
from aiofiles.threadpool.text import AsyncTextIOWrapper

from aiolifecycle import sync
from aiolifecycle import init


@init
async def json_log_path() -> str:
    # Run complicated logic to determine path, only once!
    # ....
    return '/tmp/my-file.json'


@init()
@asynccontextmanager
async def json_log_file() -> AsyncIterator[AsyncTextIOWrapper]:
    log_path = await json_log_path()
    # File will be open before any handler is called, and cleaned up on shutdown
    async with aiofiles.open(log_path, mode='a') as f:
        yield f


@sync()
async def handler():
    log_file = await json_log_file()
    await log_file.write(json.dumps(event) + "\n")
    await log_file.flush()

Changelog

v0.1.8 (2022-05-11)

Fix

• init: Fix cycle checking scope (9e76ea7)

v0.1.7 (2022-05-11)

Fix

• init: Raise terminating exception on init function failure bubbling up (69c0f88)
• init: Raise terminating exception on init function failure bubbling up (024734d)

v0.1.6 (2022-05-11)

Fix

• init: Exit immediately on init failure (8abe43b)

v0.1.5 (2022-05-11)

Fix

• init: Exit immediately on init failure (9652c7c)

v0.1.4 (2022-05-10)

Fix

• init: Fix threading atexit registration order (0a3a861)

v0.1.3 (2022-05-09)

Fix

• loop: Wait for loop on interpreter termination (e6b9825)

v0.1.2 (2022-05-09)

Fix

• init: Add missing reset for context var (#1) (fc7f654)

v0.1.1 (2022-05-05)

Fix

• license: Update copyright (588e5a3)

v0.1.0 (2022-05-05)

Feature

• all: Remove remaining lambda references (c003c73)

v0.0.4 (2022-05-05)

Fix

• handlers: Cycle detection (018ba95)
• handlers: Rename handlers to remove lambda references (de9643b)
• tests: For new resource management (5f30e6d)
• metadata: Use Markdown version of Apache License [skip ci] (bfaf82e)

v0.0.3 (2022-05-04)

Fix

• cd: Fix long_description Markdown content type (b3479ee)

v0.0.2 (2022-05-04)

Fix

• cd: Don't release on new tags (581d5ff)

v0.0.1 (2022-05-04)

Fix

• cd: Force release (7bbac93)
• cd: Force release (dd9f209)
• cd: Force release (e621555)

Copyright 2022 Daniel Miranda and contributors.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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