bands 0.1.3

Another message passing library.

bands

Another python messaging library

There are ton of python message passing / signal dispatching libraries out there. Blinker, pysignal, dispatch, pydispatcher, louie, the list goes on and on. All of these libraries are fine. This library is okay too.

Features

• bound and unbound Channels

• Pluggable Dispatchers

• Bands - groups of Channels with their own dispatcher

Working with an unbound Channel

>>> import bands

>>> def on_alert(message):
...    return message.upper()

>>> alert = bands.channel('alert')
>>> alert.connect(on_alert)
>>> alert.send('alert!!')
['ALERT!!']

Alternatively you can send your message via bands.send…

>>> bands.send('alert', 'ALERT!!')
['ALERT!!']

The send method forwards *args and **kwargs to all of the Channel’s receivers.

Working with bound Channel’s

A Channel is bound when it’s parent attribute is set. If you use bands.channel as a class attribute, each instance of your class will have it’s own bound Channel. This is very similar to the way Python methods work, except with bound Channels you’re gauranteed to get the same bound Channel instance everytime you access it.

>>> import bands

>>> class Component(object):
...     started = bands.channel('started')
...     def __init__(self, name):
...         self.name = name
...         self.started.connect(self.on_started)
...     def on_started(self):
...         return self.name + '.on_started'

>>> Component.started  # doctest:+ELLIPSIS
<unbound Channel at 0x...>(identifier='started')
>>> c1 = Component('one')
>>> c1.started  # doctest:+ELLIPSIS
<bound Channel at 0x...>(identifier='started')
>>> c2 = Component('two')
>>> c2.started  # doctest:+ELLIPSIS
<bound Channel at 0x...>(identifier='started')
>>> c1.started.send()
['one.on_started']
>>> c2.started.send()
['two.on_started']
>>> Component.started.send()
['one.on_started', 'two.on_started']
>>> bands.send('started')
['one.on_started', 'two.on_started']

From the above example, we can see that each bound Channel has it’s own subscribers. Additionally, if you call send on the unbound Channel, all bound channel receivers will also be notified. We can also use bands.send to send messages by identifier.

Working with a Band

A Band is a group of channels with a Dispatcher used to actually execute a Channel’s receivers. Messages sent to one Band will not reach another Band’s Channels or receivers.

The api functions, bands.channel and bands.send, delegate their calls to the active band. The active band defaults to the default Band accessible via the DEFAULT_BAND constant. You can set the active band with bands.use_band, and get the active band with bands.get_band. It may be wise to have a Band per application or library.

>>> import bands
>>> my_band = bands.Band()
>>> chan = my_band.channel('one')

You can also provide your own Dispatcher to my_band. Here is an example of a LoggingDispatcher.

>>> import bands
>>> import logging

>>> class LoggingDispatcher(bands.Dispatcher):
...     def __init__(self, name):
...         self.log = logging.getLogger(name)
...     def before_dispatch(self, ctx):
...         self.log.debug('Sending %s' % ctx.identifier)

>>> my_band = bands.Band(LoggingDispatcher('my_band'))

The above LoggingDispatcher will log a debug message before every message is dispatched to a channel’s receivers.

Installation

> pip install bands