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State Programming

Why, When

Very often, the response of a function will depend on the state of this object. With this pattern, It's easy to do such a thing ! You just have to write several sub-classes, each per state, inherit the State class and call the setState when the object need to change state.

Code

   1 # Code is Public Domain.
   2 class State:
   3     
   4     def setState(self,stateClass):
   5         #print stateClass.__dict__
   6         for (name,attr) in stateClass.__dict__.iteritems():
   7             if not name.startswith('_') and callable(attr):
   8                 f = getattr(stateClass,name)
   9                 l = f.__get__(self,self.__class__)
  10                 setattr(self,name,l)

Example

   1 # Code is Public Domain.
   2 class test(State):
   3     def __init__(self,a):
   4         self.a = a
   5     
   6     def showMe(self):
   7         print self.a
   8 
   9     def showYou(self,other):
  10         print self.a,other
  11 
  12     def changeToOne(self):
  13         self.setState(StateOne)
  14 
  15     def changeToTwo(self):
  16         self.setState(StateTwo)
  17 
  18 class StateOne(test):
  19 
  20     def showMe(self):
  21         print self.a,'State One'
  22 
  23     def showYou(self,other):
  24         print self.a,'State One',other
  25 
  26 class StateTwo(test):
  27 
  28     def showMe(self):
  29         print self.a,'State Two'
  30 
  31     def showYou(self,other):
  32         print self.a,'State Two',other
  33         
  34 
  35 t1 = test('t1')
  36 t2 = test('t2')
  37 t1.showMe()
  38 t2.showMe()
  39 t1.showYou("you")
  40 t1.changeToOne()
  41 t1.showMe()
  42 t2.changeToTwo()
  43 t2.showMe()
  44 t1.showYou("you")
  45 t1.changeToTwo()
  46 t2.changeToOne()
  47 t1.showMe()
  48 t2.showMe()
  49 t1.showYou("you")
  50 t2.showYou('you')

Output is

t1
t2
t1 you
t1 State One
t2 State Two
t1 State One you
t1 State Two
t2 State One
t1 State Two you
t2 State One you

StateProgramming (last edited 2008-11-15 14:00:03 by localhost)

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