mode 4.4.0
AsyncIO Service-based programming.
License: BSD
Requires Python: ~=3.6
Keywords: asyncio service bootsteps graph coroutine

=====================================================================
 Mode: AsyncIO Services
=====================================================================

|build-status| |coverage| |license| |wheel| |pyversion| |pyimp|

:Version: 4.4.0
: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:

    .. sourcecode:: console

        $ 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``:

    .. sourcecode:: console

        [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:

    .. sourcecode:: console

        $ 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.

1) Starting other services using ``add_depenency``::

    class MyService(Service):

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

2) 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),
            ]

3) 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')

4) Start a background task::

    class MyService(Service):

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


5) 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:

Installation
============

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

To install using `pip`::

    $ pip install -U mode

.. _installing-from-source:

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.

.. _installing-from-git:

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:

.. sourcecode:: console

    $ 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:

.. sourcecode:: console

    $ 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:

.. sourcecode:: text

    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/.

.. |build-status| image:: https://secure.travis-ci.org/ask/mode.png?branch=master
    :alt: Build status
    :target: https://travis-ci.org/ask/mode

.. |coverage| image:: https://codecov.io/github/ask/mode/coverage.svg?branch=master
    :target: https://codecov.io/github/ask/mode?branch=master

.. |license| image:: https://img.shields.io/pypi/l/mode.svg
    :alt: BSD License
    :target: https://opensource.org/licenses/BSD-3-Clause

.. |wheel| image:: https://img.shields.io/pypi/wheel/mode.svg
    :alt: Mode can be installed via wheel
    :target: http://pypi.org/project/mode/

.. |pyversion| image:: https://img.shields.io/pypi/pyversions/mode.svg
    :alt: Supported Python versions.
    :target: http://pypi.org/project/mode/

.. |pyimp| image:: https://img.shields.io/pypi/implementation/mode.svg
    :alt: Supported Python implementations.
    :target: http://pypi.org/project/mode/