Added the sample code from wxPython In Action to the samples dir

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42925 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

wxPython/samples/wxPIA_book/Chapter-05/abstractmodel.py

@@ -0,0 +1,15 @@
+class AbstractModel(object):
+
+    def __init__(self):
+        self.listeners = []
+
+    def addListener(self, listenerFunc):
+        self.listeners.append(listenerFunc)
+
+    def removeListener(self, listenerFunc):
+        self.listeners.remove(listenerFunc)
+
+    def update(self):
+        for eachFunc in self.listeners:
+            eachFunc(self)
+