cola/observer.py

   1 #!/usr/bin/env python
   2 # Copyright (c) 2008 David Aguilar
   3 from pprint import pformat
   4
   5 class Observer(object):
   6     """
   7     Observers receive notify(*attributes) messages from their
   8     subjects whenever new data arrives.  This notify() message signifies
   9     that an observer should update its internal state/view.
  10     """
  11
  12     def __init__(self, model):
  13         self.model = model
  14         self.model.add_observer(self)
  15         self.__debug = False
  16
  17     def __del__(self):
  18         self.model.remove_observer(self)
  19
  20     def set_debug(self, enabled):
  21         self.__debug = enabled
  22
  23     def notify(self, *attributes):
  24         """Called by the model to notify Observers about changes."""
  25         # We can be notified about multiple attribute changes at once
  26         model = self.model
  27         for attr in attributes:
  28             notify = model.get_notify()
  29             model.set_notify(False) # NOTIFY OFF
  30
  31             value = model.get_param(attr)
  32             self.subject_changed(attr, value)
  33
  34             model.set_notify(notify) # NOTIFY ON
  35
  36     def subject_changed(self, attr, value):
  37         """This method handles updating of the observer/UI.
  38         This must be implemented in each concrete observer class."""
  39
  40         msg = 'Concrete Observers must override subject_changed().'
  41         raise NotImplementedError, msg