[hello python!]Defined class method and class variable

gistfile1.py

#coding: utf-8
class Hoge
  strategy = None
  @classmethod
  def set_strategy(cls, strategy) :
    self.strategy = strategy || Piyo
  @classmethod 
  def say(cls) :
    return self.strategy.say()

class Piyo
  def say(self) :
     print "piyo"

class Fuga
  def say(self) :
     print "fuga"


#-==-=--=-=--==
Hoge.say()
=>piyo

Hoge.set_stragery(Fuga)

Hoge.say()
=>fuga