add Memento pattern

Author: JakubVojvoda

memento/Memento.py

@@ -0,0 +1,81 @@
+#
+# Python Design Patterns: Memento
+# Author: Jakub Vojvoda [github.com/JakubVojvoda]
+# 2016
+#
+# Source code is licensed under MIT License
+# (for more details see LICENSE)
+# 
+
+import sys
+
+#
+# Memento
+# stores internal state of the Originator object and protects
+# against access by objects other than the originator
+#
+class Memento:
+  def __init__(self, state):
+    self._state = state   
+
+  def setState(self, state):
+    self._state = state;
+
+  def getState(self):
+    return self._state
+  
+#
+# Originator
+# creates a memento containing a snapshot of its current internal
+# state and uses the memento to restore its internal state
+#
+class Originator:
+  def __init__(self):
+    self._state = 0
+      
+  def setState(self, state):
+    print("Set state to " + str(state) + ".")
+    self._state = state
+
+  def getState(self):
+    return self._state
+
+  def setMemento(self, memento):
+    self._state = memento.getState()
+
+  def createMemento(self):
+    return Memento(self._state)
+
+#
+# CareTaker
+# is responsible for the memento's safe keeping
+#
+class CareTaker:
+  def __init__(self, originator):
+    self._originator = originator
+    self._history = []
+
+  def save(self):
+    print("Save state.")
+    self._history.append(self._originator.createMemento())
+
+  def undo(self):
+    print("Undo state.")
+    self._originator.setMemento(self._history[-1])
+    self._history.pop()
+
+
+if __name__ == "__main__":
+  originator = Originator()
+  caretaker = CareTaker(originator)
+
+  originator.setState(1)
+  caretaker.save()
+
+  originator.setState(2)
+  caretaker.save()
+
+  originator.setState(3)
+  caretaker.undo()
+
+  print("Actual state is " + str(originator.getState()) + ".")