A simple and compact implementation of Observer design pattern
Project description
Green Rocket
Green Rocket is a simple and compact implementation of Observer (or Publish/Subscribe) design pattern via signals.
Create specific signal using base one:
>>> from greenrocket import Signal >>> class MySignal(Signal): ... pass ...
Subscribe handler:
>>> @MySignal.subscribe ... def handler(signal): ... print('handler: ' + repr(signal)) ...
Fire signal:
>>> MySignal().fire() handler: MySignal()
Note, that signal propagates over inheritance, i.e. all subscribers of base signal will be called when child one is fired:
>>> @Signal.subscribe ... def base_hadler(signal): ... print('base_handler: ' + repr(signal)) ... >>> MySignal().fire() handler: MySignal() base_handler: MySignal()
Unsubscribe handler:
>>> MySignal.unsubscribe(handler) >>> MySignal().fire() base_handler: MySignal()
The handler is subscribed using weak reference. So if you create and subscribe a handler in local scope (for example inside a generator), it will unsubscribed automatically.
>>> def gen(): ... @MySignal.subscribe ... def local_handler(signal): ... print('local_handler: ' + repr(signal)) ... yield 1 ... >>> for value in gen(): ... MySignal(value=value).fire() ... local_handler: MySignal(value=1) base_handler: MySignal(value=1) >>> import gc # PyPy fails the following test without >>> _ = gc.collect() # an explicit call of garbage collector. >>> MySignal(value=2).fire() base_handler: MySignal(value=2)
As you can see above, signal constructor accepts keyword arguments. These arguments are available as signal attributes:
>>> s = MySignal(a=1, b=2) >>> s.a 1 >>> s.b 2
Signal suppresses any exception which is raised on handler call. It uses logger named greenrocket from standard logging module to log errors and debug information.
CHANGES
0.21
Removed distribute dependency
Improved tests
0.20
Changed handler subscription mechanism from subscription by reference to subscription by weak reference
0.11
Fixed logger loose on program termination
0.1
Initial release
Project details
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