State

State encapsulates varying behavior for the same routine based on an object's state object. StateMachine imposes a structure to automatically change the implementation from one object to the next. It keeps track of the current state, which is initialized by the constructor

Ref:

1. http://en.wikipedia.org/wiki/State_pattern

2. https://python-3-patterns-idioms-test.readthedocs.org/en/latest/StateMachine.html

3. https://python-3-patterns-idioms-test.readthedocs.org/en/latest/StateMachine.html

4. http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-01sc-introduction-to-electrical-engineering-and-computer-science-i-spring-2011/unit-1-software-engineering/state-machines/MIT6_01SCS11_chap04.pdf