Mode: AsyncIO Services

Version:	4.3.2
Web:	http://mode.readthedocs.org/
Download:	http://pypi.org/project/mode
Source:	http://github.com/ask/mode
Keywords:	async, service, framework, actors, bootsteps, graph

What is Mode?

Mode is a very minimal Python library built-on top of AsyncIO that makes it much easier to use.

In Mode your program is built out of services that you can start, stop, restart and supervise.

A service is just a class:

class PageViewCache(Service):
    redis: Redis = None

    async def on_start(self) -> None:
        self.redis = connect_to_redis()

    async def update(self, url: str, n: int = 1) -> int:
        return await self.redis.incr(url, n)

    async def get(self, url: str) -> int:
        return await self.redis.get(url)

Services are started, stopped and restarted and have callbacks for those actions.

It can start another service:

class App(Service):
    page_view_cache: PageViewCache = None

    async def on_start(self) -> None:
        await self.add_runtime_dependency(self.page_view_cache)

    @cached_property
    def page_view_cache(self) -> PageViewCache:
        return PageViewCache()

It can include background tasks:

class PageViewCache(Service):

    @Service.timer(1.0)
    async def _update_cache(self) -> None:
        self.data = await cache.get('key')

Services that depends on other services actually form a graph that you can visualize.

Worker

Mode optionally provides a worker that you can use to start the program, with support for logging, blocking detection, remote debugging and more.

To start a worker add this to your program:

if __name__ == '__main__':
    from mode import Worker
    Worker(Service(), loglevel="info").execute_from_commandline()

Then execute your program to start the worker:

$ python examples/tutorial.py
[2018-03-27 15:47:12,159: INFO]: [^Worker]: Starting...
[2018-03-27 15:47:12,160: INFO]: [^-AppService]: Starting...
[2018-03-27 15:47:12,160: INFO]: [^--Websockets]: Starting...
STARTING WEBSOCKET SERVER
[2018-03-27 15:47:12,161: INFO]: [^--UserCache]: Starting...
[2018-03-27 15:47:12,161: INFO]: [^--Webserver]: Starting...
[2018-03-27 15:47:12,164: INFO]: [^--Webserver]: Serving on port 8000
REMOVING EXPIRED USERS
REMOVING EXPIRED USERS

To stop it hit Control-c:

[2018-03-27 15:55:08,084: INFO]: [^Worker]: Stopping on signal received...
[2018-03-27 15:55:08,084: INFO]: [^Worker]: Stopping...
[2018-03-27 15:55:08,084: INFO]: [^-AppService]: Stopping...
[2018-03-27 15:55:08,084: INFO]: [^--UserCache]: Stopping...
REMOVING EXPIRED USERS
[2018-03-27 15:55:08,085: INFO]: [^Worker]: Gathering service tasks...
[2018-03-27 15:55:08,085: INFO]: [^--UserCache]: -Stopped!
[2018-03-27 15:55:08,085: INFO]: [^--Webserver]: Stopping...
[2018-03-27 15:55:08,085: INFO]: [^Worker]: Gathering all futures...
[2018-03-27 15:55:08,085: INFO]: [^--Webserver]: Closing server
[2018-03-27 15:55:08,086: INFO]: [^--Webserver]: Waiting for server to close handle
[2018-03-27 15:55:08,086: INFO]: [^--Webserver]: Shutting down web application
[2018-03-27 15:55:08,086: INFO]: [^--Webserver]: Waiting for handler to shut down
[2018-03-27 15:55:08,086: INFO]: [^--Webserver]: Cleanup
[2018-03-27 15:55:08,086: INFO]: [^--Webserver]: -Stopped!
[2018-03-27 15:55:08,086: INFO]: [^--Websockets]: Stopping...
[2018-03-27 15:55:08,086: INFO]: [^--Websockets]: -Stopped!
[2018-03-27 15:55:08,087: INFO]: [^-AppService]: -Stopped!
[2018-03-27 15:55:08,087: INFO]: [^Worker]: -Stopped!

Beacons

The beacon object that we pass to services keeps track of the services in a graph.

They are not stricly required, but can be used to visualize a running system, for example we can render it as a pretty graph.

This requires you to have the pydot library and GraphViz installed:

$ pip install pydot

Let's change the app service class to dump the graph to an image at startup:

class AppService(Service):

    async def on_start(self) -> None:
        print('APP STARTING')
        import pydot
        import io
        o = io.StringIO()
        beacon = self.app.beacon.root or self.app.beacon
        beacon.as_graph().to_dot(o)
        graph, = pydot.graph_from_dot_data(o.getvalue())
        print('WRITING GRAPH TO image.png')
        with open('image.png', 'wb') as fh:
            fh.write(graph.create_png())

Creating a Service

To define a service, simply subclass and fill in the methods to do stuff as the service is started/stopped etc.:

class MyService(Service):

    async def on_start(self) -> None:
        print('Im starting now')

    async def on_started(self) -> None:
        print('Im ready')

    async def on_stop(self) -> None:
        print('Im stopping now')

To start the service, call await service.start():

await service.start()

Or you can use mode.Worker (or a subclass of this) to start your services-based asyncio program from the console:

if __name__ == '__main__':
    import mode
    worker = mode.Worker(
        MyService(),
        loglevel='INFO',
        logfile=None,
        daemon=False,
    )
    worker.execute_from_commandline()

It's a Graph!

Services can start other services, coroutines, and background tasks.

Starting other services using add_depenency:

class MyService(Service):

    def __post_init__(self) -> None:
       self.add_dependency(OtherService(loop=self.loop))

Start a list of services using on_init_dependencies:

class MyService(Service):

    def on_init_dependencies(self) -> None:
        return [
            ServiceA(loop=self.loop),
            ServiceB(loop=self.loop),
            ServiceC(loop=self.loop),
        ]

Start a future/coroutine (that will be waited on to complete on stop):

class MyService(Service):

    async def on_start(self) -> None:
        self.add_future(self.my_coro())

    async def my_coro(self) -> None:
        print('Executing coroutine')

Start a background task:

class MyService(Service):

    @Service.task
    async def _my_coro(self) -> None:
        print('Executing coroutine')

Start a background task that keeps running:

class MyService(Service):

    @Service.task
    async def _my_coro(self) -> None:
        while not self.should_stop:
            # NOTE: self.sleep will wait for one second, or
            #       until service stopped/crashed.
            await self.sleep(1.0)
            print('Background thread waking up')

Installation

You can install Mode either via the Python Package Index (PyPI) or from source.

To install using pip:

$ pip install -U mode

Downloading and installing from source

Download the latest version of Mode from http://pypi.org/project/mode

You can install it by doing the following:

$ tar xvfz mode-0.0.0.tar.gz
$ cd mode-0.0.0
$ python setup.py build
# python setup.py install

The last command must be executed as a privileged user if you are not currently using a virtualenv.

Using the development version

With pip

You can install the latest snapshot of Mode using the following pip command:

$ pip install https://github.com/ask/mode/zipball/master#egg=mode

FAQ

Can I use Mode with Django/Flask/etc.?

Yes! Use gevent/eventlet as a bridge to integrate with asyncio.

Using `gevent`

This works with any blocking Python library that can work with gevent.

Using gevent requires you to install the aiogevent module, and you can install this as a bundle with Mode:

$ pip install -U mode[gevent]

Then to actually use gevent as the event loop you have to execute the following in your entrypoint module (usually where you start the worker), before any other third party libraries are imported:

#!/usr/bin/env python3
import mode.loop
mode.loop.use('gevent')
# execute program

REMEMBER: This must be located at the very top of the module, in such a way that it executes before you import other libraries.

Using `eventlet`

This works with any blocking Python library that can work with eventlet.

Using eventlet requires you to install the aioeventlet module, and you can install this as a bundle with Mode:

$ pip install -U mode[eventlet]

Then to actually use eventlet as the event loop you have to execute the following in your entrypoint module (usually where you start the worker), before any other third party libraries are imported:

#!/usr/bin/env python3
import mode.loop
mode.loop.use('eventlet')
# execute program

REMEMBER: It's very important this is at the very top of the module, and that it executes before you import libraries.

Can I use Mode with Tornado?

Yes! Use the tornado.platform.asyncio bridge: http://www.tornadoweb.org/en/stable/asyncio.html

Can I use Mode with Twisted?

Yes! Use the asyncio reactor implementation: https://twistedmatrix.com/documents/17.1.0/api/twisted.internet.asyncioreactor.html

Will you support Python 3.5 or earlier?

There are no immediate plans to support Python 3.5, but you are welcome to contribute to the project.

Here are some of the steps required to accomplish this:

Source code transformation to rewrite variable annotations to comments

for example, the code:

     class Point:
         x: int = 0
         y: int = 0

must be rewritten into::

     class Point:
         x = 0  # type: int
         y = 0  # type: int

Source code transformation to rewrite async functions

for example, the code:

async def foo():
    await asyncio.sleep(1.0)

must be rewritten into:

@coroutine
def foo():
    yield from asyncio.sleep(1.0)

Will you support Python 2?

There are no plans to support Python 2, but you are welcome to contribute to the project (details in question above is relevant also for Python 2).

At Shutdown I get lots of warnings, what is this about?

If you get warnings such as this at shutdown:

Task was destroyed but it is pending!
task: <Task pending coro=<Service._execute_task() running at /opt/devel/mode/mode/services.py:643> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0x1100a7468>()]>>
Task was destroyed but it is pending!
task: <Task pending coro=<Service._execute_task() running at /opt/devel/mode/mode/services.py:643> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0x1100a72e8>()]>>
Task was destroyed but it is pending!
task: <Task pending coro=<Service._execute_task() running at /opt/devel/mode/mode/services.py:643> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0x1100a7678>()]>>
Task was destroyed but it is pending!
task: <Task pending coro=<Event.wait() running at /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/locks.py:269> cb=[_release_waiter(<Future pendi...1100a7468>()]>)() at /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/tasks.py:316]>
Task was destroyed but it is pending!
    task: <Task pending coro=<Event.wait() running at /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/locks.py:269> cb=[_release_waiter(<Future pendi...1100a7678>()]>)() at /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/tasks.py:316]>

It usually means you forgot to stop a service before the process exited.

Code of Conduct

Everyone interacting in the project's codebases, issue trackers, chat rooms, and mailing lists is expected to follow the Mode Code of Conduct.

As contributors and maintainers of these projects, and in the interest of fostering an open and welcoming community, we pledge to respect all people who contribute through reporting issues, posting feature requests, updating documentation, submitting pull requests or patches, and other activities.

We are committed to making participation in these projects a harassment-free experience for everyone, regardless of level of experience, gender, gender identity and expression, sexual orientation, disability, personal appearance, body size, race, ethnicity, age, religion, or nationality.

Examples of unacceptable behavior by participants include:

The use of sexualized language or imagery
Personal attacks
Trolling or insulting/derogatory comments
Public or private harassment
Publishing other's private information, such as physical or electronic addresses, without explicit permission
Other unethical or unprofessional conduct.

Project maintainers have the right and responsibility to remove, edit, or reject comments, commits, code, wiki edits, issues, and other contributions that are not aligned to this Code of Conduct. By adopting this Code of Conduct, project maintainers commit themselves to fairly and consistently applying these principles to every aspect of managing this project. Project maintainers who do not follow or enforce the Code of Conduct may be permanently removed from the project team.

This code of conduct applies both within project spaces and in public spaces when an individual is representing the project or its community.

Instances of abusive, harassing, or otherwise unacceptable behavior may be reported by opening an issue or contacting one or more of the project maintainers.

This Code of Conduct is adapted from the Contributor Covenant, version 1.2.0 available at http://contributor-covenant.org/version/1/2/0/.

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