broqer 2.0.3

Carefully crafted library to operate with continuous streams of data in a reactive style with publish/subscribe and broker functionality.

Initial focus on embedded systems Broqer can be used wherever continuous streams of data have to be processed - and they are everywhere. Watch out!

Synopsis

• Pure python implementation without dependencies

• Under MIT license (2018 Günther Jena)

• Source is hosted on GitHub.com

• Documentation is hosted on ReadTheDocs.com

• Tested on Python 3.5, 3.6, 3.7. 3.8 and 3.9

• Unit tested with pytest, coding style checked with Flake8, static type checked with mypy, static code checked with Pylint, documented with Sphinx

• Operators known from ReactiveX and other streaming frameworks (like Map, CombineLatest, …)

  • Centralised object to keep track of publishers and subscribers

  • Starting point to build applications with a microservice architecture

Showcase

In other frameworks a Publisher is sometimes called Oberservable. A Subscriber is able to observe changes the publisher is emitting. With these basics you’re able to use the observer pattern - let’s see!

Observer pattern

Subscribing to a publisher is done via the .subscribe() method. A simple subscriber is Sink which is calling a function with optional positional and keyword arguments.

>>> from broqer import Publisher, Sink
>>> a = Publisher(5)  # create a publisher with state `5`
>>> s = Sink(print, 'Change:')  # create a subscriber
>>> disposable = a.subscribe(s)  # subscribe subscriber to publisher
Change: 5

>>> a.notify(3)  # change the state
Change: 3

>>> disposable.dispose()  # unsubscribe

Combine publishers with arithmetic operators

You’re able to create publishers on the fly by combining two publishers with the common operators (like +, >, <<, …).

>>> a = Publisher(1)
>>> b = Publisher(3)

>>> c = a * 3 > b  # create a new publisher via operator overloading
>>> disposable = c.subscribe(Sink(print, 'c:'))
c: False

>>> a.notify(2)
c: True

>>> b.notify(10)
c: False

Also fancy stuff like getting item by index or key is possible:

>>> i = Publisher('a')
>>> d = Publisher({'a':100, 'b':200, 'c':300})

>>> disposable = d[i].subscribe(Sink(print, 'r:'))
r: 100

>>> i.notify('c')
r: 300
>>> d.notify({'c':123})
r: 123

Some python built in functions can’t return Publishers (e.g. len() needs to return an integer). For these cases special functions are defined in broqer: Str, Int, Float, Len and In (for x in y). Also other functions for convenience are available: All, Any, BitwiseAnd and BitwiseOr.

Attribute access on a publisher is building a publisher where the actual attribute access is done on emitting values. A publisher has to know, which type it should mimic - this is done via .inherit_type(type).

>>> i = Publisher('Attribute access made REACTIVE')
>>> i.inherit_type(str)
>>> disposable = i.lower().split(sep=' ').subscribe(Sink(print))
['attribute', 'access', 'made', 'reactive']

>>> i.notify('Reactive and pythonic')
['reactive', 'and', 'pythonic']

Function decorators

Make your own operators on the fly with function decorators. Decorators are available for Accumulate, CombineLatest, Filter, Map, MapAsync, MapThreaded, Reduce and Sink.

>>> from broqer import op
>>> @op.build_map
... def count_vowels(s):
...     return sum([s.count(v) for v in 'aeiou'])

>>> msg = Publisher('Hello World!')
>>> disposable = (msg | count_vowels).subscribe(Sink(print, 'Number of vowels:'))
Number of vowels: 3
>>> msg.notify('Wahuuu')
Number of vowels: 4

You can even make configurable Map s and Filter s:

>>> import re

>>> @op.build_filter_factory
... def filter_pattern(pattern, s):
...     return re.search(pattern, s) is not None

>>> msg = Publisher('Cars passed: 135!')
>>> disposable = (msg | filter_pattern('[0-9]+')).subscribe(Sink(print))
Cars passed: 135!
>>> msg.notify('No cars have passed')
>>> msg.notify('Only 1 car has passed')
Only 1 car has passed

Install

pip install broqer

Credits

Broqer was inspired by:

• RxPY: Reactive Extension for Python (by Børge Lanes and Dag Brattli)

• aioreactive: Async/Await reactive tools for Python (by Dag Brattli)

• streamz: build pipelines to manage continuous streams of data (by Matthew Rocklin)

• MQTT: M2M connectivity protocol

• Florian Feurstein: spending hours of discussion, coming up with great ideas and help me understand the concepts!

API

Publishers

A Publisher is the source for messages.

Publisher ()

Basic publisher

Operators

CombineLatest (*publishers)	Combine the latest emit of multiple publishers and emit the combination
Filter (predicate, …)	Filters values based on a predicate function
Map (map_func, *args, **kwargs)	Apply map_func(*args, value, **kwargs) to each emitted value
MapAsync (coro, mode, …)	Apply coro(*args, value, **kwargs) to each emitted value

Subscribers

A Subscriber is the sink for messages.

Sink (func, *args, **kwargs)	Apply func(*args, value, **kwargs) to each emitted value
SinkAsync (coro, …)	Apply coro(*args, value, **kwargs) to each emitted value
OnEmitFuture (timeout=None)	Build a future able to await for
Trace (d)	Debug output for publishers

Values

Value (*init)

Publisher and Subscriber