cola/observable.py

   1 # Copyright (c) 2008 David Aguilar
   2 """This module provides the Observable class"""
   3
   4 import types
   5
   6 class Observable(object):
   7     """Handles subject/observer notifications."""
   8     def __init__(self):
   9         self.observers = set()
  10         self.message_observers = {}
  11         self.notification_enabled = True
  12         self.register_messages()
  13
  14     def register_messages(self, messages=None):
  15         """
  16         Automatically register all class-scope message names.
  17
  18         There are two rules at play here:
  19
  20         1. Message names must be defined at class scope. e.g.:
  21
  22             class ObservableFoo(Observable):
  23                 message_foo = 'foo'
  24
  25         2. Message name variables must begin with the string 'message_'
  26
  27         Providing a 'messages' dict avoids this built-in behavior but
  28         does not guarantee that the messages names are registered for
  29         clones or unserialized objects.
  30
  31         """
  32         if messages:
  33             self.message_observers.update(messages)
  34         else:
  35             for k, v in self.__class__.__dict__.iteritems():
  36                 if k.startswith('message_') and type(v) in types.StringTypes:
  37                     self.message_observers[v] = set()
  38
  39     def add_observer(self, observer):
  40         """Adds an observer to this model"""
  41         self.observers.add(observer)
  42
  43     def add_message_observer(self, message, observer):
  44         """Add an observer for a specific message."""
  45         observers = self.message_observers.setdefault(message, set())
  46         observers.add(observer)
  47
  48     def remove_observer(self, observer):
  49         """Removes an observer"""
  50         if observer in self.observers:
  51             self.observers.remove(observer)
  52         for message, observers in self.message_observers.items():
  53             if observer in observers:
  54                 observers.remove(observer)
  55
  56     def notify_observers(self, *param):
  57         """Notifies observers about attribute changes"""
  58         if not self.notification_enabled:
  59             return
  60         for observer in self.observers:
  61             observer.notify(*param)
  62
  63     def notify_message_observers(self, message, *args, **opts):
  64         """Pythonic signals and slots."""
  65         if not self.notification_enabled:
  66             return
  67         if message not in self.message_observers:
  68             raise ValueError('%s is not a valid message name.' % message)
  69         observers = self.message_observers[message]
  70         for method in observers:
  71             method(*args, **opts)