ugitlibs/observer.py

   1 #!/usr/bin/env python
   2 from pprint import pformat
   3
   4 class Observer(object):
   5         '''Observers receive notify(*attributes) messages from their
   6         subjects whenever new data arrives.  This notify() message signifies
   7         that an observer should update its internal state/view.'''
   8
   9         def __init__(self, model):
  10                 self.model = model
  11                 self.model.add_observer(self)
  12
  13                 self.__attribute_adapter = {}
  14                 self.__subjects = []
  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                 for attr in attributes:
  27
  28                         if attr not in self.__subjects: continue
  29
  30                         # The new value for updating
  31                         model = self.model
  32                         notify = model.get_notify()
  33                         model.set_notify(False)
  34                         value = model.getattr(attr)
  35
  36                         # Allow lazy model to observer attributes renames
  37                         if attr in self.__attribute_adapter:
  38                                 attr = self.__attribute_adapter[attr]
  39
  40                         # Call the concrete observer's notification method
  41                         self.subject_changed(attr, value)
  42
  43                         model.set_notify(notify)
  44
  45                         if not self.__debug: continue
  46                         print("Objserver::notify("+ pformat(attributes) +"):")
  47                         print model
  48
  49         def subject_changed(self, attr, value):
  50                 '''This method handles updating of the observer/UI.
  51                 This must be implemented in each concrete observer class.'''
  52
  53                 msg = 'Concrete Observers must override subject_changed().'
  54                 raise NotImplementedError, msg
  55
  56         def add_subject(self, model_attr):
  57                 self.__subjects.append(model_attr)
  58
  59         def add_attribute_adapter(self, model_attr, observer_attr):
  60                 self.__attribute_adapter[model_attr] = observer_attr