python优雅实现策略模式

优雅实现策略模式; 在awesome-python上有一个关于模式设计的包，对包中的代码做了一点修改。BaseStrateby最核心的方法是select.

# -*- coding: utf-8 -*-"""http://stackoverflow.com/questions/963965/how-is-this-strategy-pattern -written-in-python-the-sample-in-wikipediaIn most of other languages Strategy pattern is implemented via creating somebase strategy interface/abstract class and subclassing it with a number ofconcrete strategies (as we can see athttp://en.wikipedia.org/wiki/Strategy_pattern), however Python supportshigher-order functions and allows us to have only one class and injectfunctions into it's instances, as shown in this example."""import typesimport randomclass BaseStrategy:    def __init__(self, func=None):        if func is not None:            self.select(func)    def __call__(self, *args, **kwargs):        self.execute(*args, **kwargs)    def execute(self, *args, **kwargs):        pass    def select(self, func):        # redefine a method        self.execute = types.MethodType(func, self)class StrategyExample(BaseStrategy):    def __init__(self, func=None):        self.name = 'Strategy Example 0'        if func is not None:            self.select(func)    def execute(self, arg='nothing'):        print(arg)    def make(self):        self.select(execute_replacement1)    def random(self):        r = random.random()        if r > 0.5:            self.select(execute_replacement1)        else:            self.select(execute_replacement2)# strategiesdef execute_replacement1(obj, s=' from execute'):    print(obj.name + s + '1')def execute_replacement2(obj, s=' from execute'):    print(obj.name + s + '2')class SubStrategy(StrategyExample):    def __init__(self, func=None):        super(SubStrategy, self).__init__(func)        self.name = 'Strategy Example x'if __name__ == '__main__':    strat0 = StrategyExample()    stratx = SubStrategy()    stratx()    strat1 = StrategyExample(execute_replacement1)    strat1.name = 'Strategy Example 1'    strat2 = StrategyExample(execute_replacement2)    strat2.name = 'Strategy Example 2'    strat0()    strat1()    strat2()    strat2.select(execute_replacement1)    strat2()        for k  in range(5):        stratx = SubStrategy()        stratx.random()        stratx('shit')### OUTPUT #### nothing# nothing# Strategy Example 1 from execute 1# Strategy Example 2 from execute 2# Strategy Example 2 from execute 1# Strategy Example xshit# Strategy Example xshit# Strategy Example xshit# Strategy Example xshit# Strategy Example xshit