Implemented the observer pattern.

pypatterns/behavioral/observer.py

@@ -0,0 +1,55 @@
+from abc import ABCMeta, abstractmethod
+
+
+class Observer(object, metaclass=ABCMeta):
+    """
+    Abstract Observer class as part of the Observer design pattern.
+    """
+    @abstractmethod
+    def update(self, **state):
+        """
+        Abstract method that is called when an Observable's state changes.
+        """
+        pass
+
+
+class Observable(object):
+    """
+    Base Observable class as part of the Observer design pattern
+    """
+    def __init__(self):
+        """
+        Initialize a new Observable instance.
+        """
+        self._observers = set()
+
+    def attach(self, observer):
+        """
+        Attach an observer to this Observable.
+
+        @param observer: The Observer to attach.
+        @type observer: Observer
+        """
+        self._observers.add(observer)
+
+    def detach(self, observer):
+        """
+        Detach an observer from this Observable.
+
+        @param observer: The Observer to detach.
+        @type observer: Observer
+        """
+        try:
+            self._observers.remove(observer)
+        except KeyError:
+            pass
+
+    def notify(self):
+        """
+        Notify all attached Observers of the state of this Observable.
+        This should be called when this Observable's state changes.
+        """
+        for observer in self._observers:
+            state = {k: v for k, v in self.__dict__.items() if not k.startswith('__') and not k.startswith('_')}
+            observer.update(**state)
+