new tasks

Task/Delegates/Python/delegates.py

@@ -0,0 +1,25 @@
+class Delegator:
+   def __init__(self):
+      self.delegate = None
+   def operation(self):
+       if hasattr(self.delegate, 'thing') and callable(self.delegate.thing):
+          return self.delegate.thing()
+       return 'default implementation'
+
+class Delegate:
+   def thing(self):
+      return 'delegate implementation'
+
+if __name__ == '__main__':
+
+   # No delegate
+   a = Delegator()
+   assert a.operation() == 'default implementation'
+
+   # With a delegate that does not implement "thing"
+   a.delegate = 'A delegate may be any object'
+   assert a.operation() == 'default implementation'
+
+   # With delegate that implements "thing"
+   a.delegate = Delegate()
+   assert a.operation() == 'delegate implementation'