# 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:

app = faust.App('myapp', broker='kafka:https://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 superfast 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:

# data sent to 'clicks' topic sharded by URL key.
# e.g. key="https://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:

# 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.

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:https://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, Scikit, TensorFlow, etc.

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

To install using pip:

$ pip install -U faust

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:

$ pip install "faust[rocksdb]"

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

The following bundles are available:

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

You can install it by doing:

$ 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.

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

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

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

This approach 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 Faust:

$ pip install -U faust[gevent]

Then to actually use gevent as the event loop you have to either use the -L <faust --loop> option to the faust program:

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

or add import mode.loop.gevent at the top of your entry point script:

#!/usr/bin/env python3
import mode.loop.gevent

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

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:

$ pip install -U faust[eventlet]

Then to actually use eventlet as the event loop you have to either use the -L <faust --loop> argument to the faust program:

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

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

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

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

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

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)
  

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

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/

Faust supports kafka with version >= 0.10.

For discussions about the usage, development, and future of Faust, please join the faust-users mailing list.

Come chat with us on Slack:

https://join.slack.com/t/fauststream/shared_invite/enQtNDEzMTIyMTUyNzU2LTRkM2Q2ODkwZTk5MzczNmUxOGU0NWYxNzA2YzYwNTAyZmRiOTRmMzkyMDk0ODY2MjIzOTg2NGI0ODlmNTYxNTc

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

https://wiki.github.com/robinhood/faust/

This software is licensed under the New BSD License. See the LICENSE file in the top distribution directory for the full license text.

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.

Everyone interacting in the project's codebases, 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 1.4.2 available at https://contributor-covenant.org/version/1/2/0/.