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robinhood
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Python Stream Processing

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===========================

Python Stream Processing

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

:Version: 1.10.4 :Web: http://faust.readthedocs.io/ :Download: http://pypi.org/project/faust :Source: http://github.com/robinhood/faust :Keywords: distributed, stream, async, processing, data, queue, state management

.. sourcecode:: python

# Python Streams
# Forever scalable event processing & in-memory durable K/V store;
# as a library w/ asyncio & static typing.
import faust

Faust is a stream processing library, porting the ideas from

Kafka Streams
_ to Python.

It is used at

Robinhood
_ to build high performance distributed systems and real-time data pipelines that process billions of events every day.

Faust provides both stream processing and event processing, sharing similarity with tools such as

Kafka Streams
,
Apache Spark
/
Storm
/
Samza
/
Flink
_,

It does not use a DSL, it's just Python! This means you can use all your favorite Python libraries when stream processing: NumPy, PyTorch, Pandas, NLTK, Django, Flask, SQLAlchemy, ++

Faust requires Python 3.6 or later for the new

async/await
_ syntax, and variable type annotations.

Here's an example processing a stream of incoming orders:

.. sourcecode:: python

app = faust.App('myapp', broker='kafka://localhost')

Models describe how messages are serialized:

{"account_id": "3fae-...", amount": 3}

class Order(faust.Record): account_id: str amount: int

@app.agent(value_type=Order) async def order(orders): async for order in orders: # process infinite stream of orders. print(f'Order for {order.account_id}: {order.amount}')

The Agent decorator defines a "stream processor" that essentially consumes from a Kafka topic and does something for every event it receives.

The agent is an

async def
function, so can also perform other operations asynchronously, such as web requests.

This system can persist state, acting like a database. Tables are named distributed key/value stores you can use as regular Python dictionaries.

Tables are stored locally on each machine using a super fast embedded database written in C++, called

RocksDB
_.

Tables can also store aggregate counts that are optionally "windowed" so you can keep track of "number of clicks from the last day," or "number of clicks in the last hour." for example. Like

Kafka Streams
_, we support tumbling, hopping and sliding windows of time, and old windows can be expired to stop data from filling up.

For reliability we use a Kafka topic as "write-ahead-log". Whenever a key is changed we publish to the changelog. Standby nodes consume from this changelog to keep an exact replica of the data and enables instant recovery should any of the nodes fail.

To the user a table is just a dictionary, but data is persisted between restarts and replicated across nodes so on failover other nodes can take over automatically.

You can count page views by URL:

.. sourcecode:: python

# data sent to 'clicks' topic sharded by URL key.
# e.g. key="http://example.com" value="1"
click_topic = app.topic('clicks', key_type=str, value_type=int)

default value for missing URL will be 0 with default=int

counts = app.Table('click_counts', default=int)

@app.agent(click_topic) async def count_click(clicks): async for url, count in clicks.items(): counts[url] += count

The data sent to the Kafka topic is partitioned, which means the clicks will be sharded by URL in such a way that every count for the same URL will be delivered to the same Faust worker instance.

Faust supports any type of stream data: bytes, Unicode and serialized structures, but also comes with "Models" that use modern Python syntax to describe how keys and values in streams are serialized:

.. sourcecode:: python

# Order is a json serialized dictionary,
# having these fields:

class Order(faust.Record): account_id: str product_id: str price: float quantity: float = 1.0

orders_topic = app.topic('orders', key_type=str, value_type=Order)

@app.agent(orders_topic) async def process_order(orders): async for order in orders: # process each order using regular Python total_price = order.price * order.quantity await send_order_received_email(order.account_id, order)

Faust is statically typed, using the

mypy
type checker, so you can take advantage of static types when writing applications.

The Faust source code is small, well organized, and serves as a good resource for learning the implementation of

Kafka Streams
_.

Learn more about Faust in the

introduction
_ introduction page to read more about Faust, system requirements, installation instructions, community resources, and more.

or go directly to the

quickstart
_ tutorial to see Faust in action by programming a streaming application.

then explore the

User Guide
_ for in-depth information organized by topic.

.. _

Robinhood
: http://robinhood.com .. _
async/await
: https://medium.freecodecamp.org/a-guide-to-asynchronous-programming-in-python-with-asyncio-232e2afa44f6 .. _
Celery
: http://celeryproject.org .. _
Kafka Streams
: https://kafka.apache.org/documentation/streams .. _
Apache Spark
: http://spark.apache.org .. _
Storm
: http://storm.apache.org .. _
Samza
: http://samza.apache.org .. _
Flink
: http://flink.apache.org .. _
RocksDB
: http://rocksdb.org .. _
Apache Kafka
: https://kafka.apache.org

.. _

introduction
: http://faust.readthedocs.io/en/latest/introduction.html

.. _

quickstart
: http://faust.readthedocs.io/en/latest/playbooks/quickstart.html

.. _

User Guide
: http://faust.readthedocs.io/en/latest/userguide/index.html

Faust is...

Simple Faust is extremely easy to use. To get started using other stream processing solutions you have complicated hello-world projects, and infrastructure requirements. Faust only requires Kafka, the rest is just Python, so If you know Python you can already use Faust to do stream processing, and it can integrate with just about anything.

Here's one of the easier applications you can make::

import faust

class Greeting(faust.Record):
    from_name: str
    to_name: str

app = faust.App('hello-app', broker='kafka://localhost')
topic = app.topic('hello-topic', value_type=Greeting)

@app.agent(topic)
async def hello(greetings):
    async for greeting in greetings:
        print(f'Hello from {greeting.from_name} to {greeting.to_name}')

@app.timer(interval=1.0)
async def example_sender(app):
    await hello.send(
        value=Greeting(from_name='Faust', to_name='you'),
    )

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

You're probably a bit intimidated by the async and await keywords, but you don't have to know how asyncio works to use Faust: just mimic the examples, and you'll be fine.

The example application starts two tasks: one is processing a stream, the other is a background thread sending events to that stream. In a real-life application, your system will publish events to Kafka topics that your processors can consume from, and the background thread is only needed to feed data into our example.

Highly Available Faust is highly available and can survive network problems and server crashes. In the case of node failure, it can automatically recover, and tables have standby nodes that will take over.

Distributed Start more instances of your application as needed.

Fast A single-core Faust worker instance can already process tens of thousands of events every second, and we are reasonably confident that throughput will increase once we can support a more optimized Kafka client.

Flexible Faust is just Python, and a stream is an infinite asynchronous iterator. If you know how to use Python, you already know how to use Faust, and it works with your favorite Python libraries like Django, Flask, SQLAlchemy, NTLK, NumPy, SciPy, TensorFlow, etc.

.. _

introduction
: http://faust.readthedocs.io/en/latest/introduction.html

.. _

quickstart
: http://faust.readthedocs.io/en/latest/playbooks/quickstart.html

.. _

User Guide
: http://faust.readthedocs.io/en/latest/userguide/index.html

Installation

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

To install using

pip
:

.. sourcecode:: console

$ pip install -U faust

.. _bundles:

Bundles

Faust also defines a group of

setuptools
extensions that can be used to install Faust and the dependencies for a given feature.

You can specify these in your requirements or on the

pip
command-line by using brackets. Separate multiple bundles using the comma:

.. sourcecode:: console

$ pip install "faust[rocksdb]"

$ pip install "faust[rocksdb,uvloop,fast,redis]"

The following bundles are available:

Stores ~~~~~~

:

faust[rocksdb]
: for using
RocksDB
_ for storing Faust table state.
**Recommended in production.**

.. _

RocksDB
: http://rocksdb.org

Caching ~~~~~~~

:

faust[redis]
: for using
Redis_
as a simple caching backend (Memcached-style).

Codecs ~~~~~~

:

faust[yaml]
: for using YAML and the
PyYAML
library in streams.

Optimization ~~~~~~~~~~~~

:

faust[fast]
: for installing all the available C speedup extensions to Faust core.

Sensors ~~~~~~~

:

faust[datadog]
: for using the Datadog Faust monitor.

:

faust[statsd]
: for using the Statsd Faust monitor.

Event Loops ~~~~~~~~~~~

:

faust[uvloop]
: for using Faust with
uvloop
.

:

faust[eventlet]
: for using Faust with
eventlet

Debugging ~~~~~~~~~

:

faust[debug]
: for using
aiomonitor
to connect and debug a running Faust worker.

:

faust[setproctitle]
: when the
setproctitle
module is installed the Faust worker will use it to set a nicer process name in
ps
/
top
listings. Also installed with the
fast
and
debug
bundles.

Downloading and installing from source

Download the latest version of Faust from http://pypi.org/project/faust

You can install it by doing:

.. sourcecode:: console

$ tar xvfz faust-0.0.0.tar.gz
$ cd faust-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 Faust using the following

pip
command:

.. sourcecode:: console

$ pip install https://github.com/robinhood/faust/zipball/master#egg=faust

.. _

introduction
: http://faust.readthedocs.io/en/latest/introduction.html

.. _

quickstart
: http://faust.readthedocs.io/en/latest/playbooks/quickstart.html

.. _

User Guide
: http://faust.readthedocs.io/en/latest/userguide/index.html

FAQ

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

Yes! Use

eventlet
as a bridge to integrate with
asyncio
.

Using

eventlet
~~~~~~~~~~~~~~~~~~~~~~

This approach 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 along with Faust:

.. sourcecode:: console

$ pip install -U faust[eventlet]

Then to actually use eventlet as the event loop you have to either use the

-L 
argument to the
faust
program:

.. sourcecode:: console

$ faust -L eventlet -A myproj worker -l info

or add

import mode.loop.eventlet
at the top of your entry point script:

.. sourcecode:: python

#!/usr/bin/env python3
import mode.loop.eventlet  # noqa

.. warning::

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

Can I use Faust with Tornado?

Yes! Use the

tornado.platform.asyncio
bridge: http://www.tornadoweb.org/en/stable/asyncio.html

Can I use Faust with Twisted?

Yes! Use the

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

Will you support Python 2.7 or Python 3.5?

No. Faust requires Python 3.6 or later, since it heavily uses features that were introduced in Python 3.6 (

async
,
await
, variable type annotations).

I get a maximum number of open files exceeded error by RocksDB when running a Faust app locally. How can I fix this?

You may need to increase the limit for the maximum number of open files. The following post explains how to do so on OS X: https://blog.dekstroza.io/ulimit-shenanigans-on-osx-el-capitan/

What kafka versions faust supports?

Faust supports kafka with version >= 0.10.

.. _

introduction
: http://faust.readthedocs.io/en/latest/introduction.html

.. _

quickstart
: http://faust.readthedocs.io/en/latest/playbooks/quickstart.html

.. _

User Guide
: http://faust.readthedocs.io/en/latest/userguide/index.html

.. _getting-help:

Getting Help

.. _slack-channel:

Slack

For discussions about the usage, development, and future of Faust, please join the

fauststream
_ Slack.
  • https://fauststream.slack.com
  • Sign-up: https://join.slack.com/t/fauststream/shared_invite/enQtNDEzMTIyMTUyNzU2LTIyMjNjY2M2YzA2OWFhMDlmMzVkODk3YTBlYThlYmZiNTUwZDJlYWZiZTdkN2Q4ZGU4NWM4YWMyNTM5MGQ5OTg

Resources

.. _bug-tracker:

Bug tracker

If you have any suggestions, bug reports, or annoyances please report them to our issue tracker at https://github.com/robinhood/faust/issues/

.. _license:

License

This software is licensed under the

New BSD License
. See the
LICENSE
file in the top distribution directory for the full license text.

.. # vim: syntax=rst expandtab tabstop=4 shiftwidth=4 shiftround

.. _

introduction
: http://faust.readthedocs.io/en/latest/introduction.html

.. _

quickstart
: http://faust.readthedocs.io/en/latest/playbooks/quickstart.html

.. _

User Guide
: http://faust.readthedocs.io/en/latest/userguide/index.html

Contributing

Development of

Faust
happens at GitHub: https://github.com/robinhood/faust

You're highly encouraged to participate in the development of

Faust
.

Be sure to also read the

Contributing to Faust
_ section in the documentation.

.. _

Contributing to Faust
: http://faust.readthedocs.io/en/latest/contributing.html

Code of Conduct

Everyone interacting in the project's code bases, issue trackers, chat rooms, and mailing lists is expected to follow the Faust 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/.

.. _

introduction
: http://faust.readthedocs.io/en/latest/introduction.html

.. _

quickstart
: http://faust.readthedocs.io/en/latest/playbooks/quickstart.html

.. _

User Guide
: http://faust.readthedocs.io/en/latest/userguide/index.html

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

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

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

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

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

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

.. _

introduction
: http://faust.readthedocs.io/en/latest/introduction.html

.. _

quickstart
: http://faust.readthedocs.io/en/latest/playbooks/quickstart.html

.. _

User Guide
: http://faust.readthedocs.io/en/latest/userguide/index.html

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