python-patterns/strategy.py

"""http://stackoverflow.com/questions/963965/how-is-this-strategy-pattern-written-in-python-the-sample-in-wikipedia

In most of other languages Strategy pattern is implemented via creating some base strategy interface/abstract class and
subclassing it with a number of concrete strategies (as we can see at http://en.wikipedia.org/wiki/Strategy_pattern),
however Python supports higher-order functions and allows us to have only one class and inject functions into it's
instances, as shown in this example.
"""
import types


class StrategyExample:
    def __init__(self, func=None):
        self.name = 'Strategy Example 0'         
        if func is not None:
            self.execute = types.MethodType(func, self)      

    def execute(self):         
        print(self.name)   


def execute_replacement1(self):
    print(self.name + ' from execute 1')   


def execute_replacement2(self):
    print(self.name + ' from execute 2')  


if __name__ == '__main__':
    strat0 = StrategyExample()     

    strat1 = StrategyExample(execute_replacement1)
    strat1.name = 'Strategy Example 1'     

    strat2 = StrategyExample(execute_replacement2)
    strat2.name = 'Strategy Example 2'

    strat0.execute()
    strat1.execute()     
    strat2.execute()