strategy.py

"""
Strategy pattern - we have a default method, we can change its behaviour with another function at run time.

It is easy to implement with Python with its build-in "types" module.
"""


import types


class Strategy:
    """The Strategy Pattern class"""
    def __init__(self, function=None):
        self.name = "Default Strategy"

        # If a reference to a function is provided, replace the execute() method with the given function
        if function:
            self.execute = types.MethodType(function, self)

    def execute(self):  # This gets replaced by another version if another strategy is provided.
        """The default method that prints the name of the strategy being used"""
        print("{} is used!".format(self.name))


def strategy_one(self):
    print("{} is used to execute method 1".format(self.name))


def strategy_two(self):
    print("{} is used to execute method 2".format(self.name))


def main():
    # Let's create our default strategy
    s0 = Strategy()
    s0.execute()

    s1 = Strategy(strategy_one)
    s1.name = "Strategy One"
    s1.execute()

    s2 = Strategy(strategy_two)
    s2.name = "Strategy Two"
    s2.execute()


if __name__ == "__main__":
    main()