Strategy Design Pattern in Python I'm reading the awesome Head First Design Patterns book. As an exercise I converted first example (or rather a subset of it) to Python. The code I got is rather too simple, i.e. there is no abstract nor interface declarations, it's all just 'classes'. Is that the right way to do it in Python? My code is below, original Java code and problem statement can be found at http://books.google.com/books?id=LjJcCnNf92kC&amp;pg=PA18

class QuackBehavior():
    def __init__(self):
        pass
    def quack(self):
        pass

class Quack(QuackBehavior):
    def quack(self):
        print "Quack!"

class QuackNot(QuackBehavior):
    def quack(self):
        print "..."

class Squeack(QuackBehavior):
    def quack(self):
        print "Squeack!"

class FlyBehavior():
    def fly(self):
        pass

class Fly():
    def fly(self):
        print "I'm flying!"

class FlyNot():
    def fly(self):
        print "Can't fly..."

class Duck():
    def display(self):
        print this.name

    def performQuack(self):
        self.quackBehavior.quack()

    def performFly(self):
        self.flyBehavior.fly()

class MallardDuck(Duck):
    def __init__(self):
        self.quackBehavior = Quack()
        self.flyBehavior = Fly()

if __name__ == "__main__":
    mallard = MallardDuck()
    mallard.performQuack()
    mallard.performFly()
    mallard.flyBehavior = FlyNot()
    mallard.performFly()
class QuackBehavior():


Don't put () after classes, either skip it, or put object in there

    def __init__(self):
        pass


There's no reason to define a constructor if you aren't going to do anything, so just skip  it

    def quack(self):
        pass


You should probably at least raise NotImplementedError(), so that if anyone tries to call this it'll complain. That'll also make it clear what this class is doing.

You don't really need this class at all. The only reason to provide classes like this in python is documentation purposes. Whether or not you think that's useful enough is up to you.

class Quack(QuackBehavior):
    def quack(self):
        print "Quack!"

class QuackNot(QuackBehavior):
    def quack(self):
        print "..."

class Squeack(QuackBehavior):
    def quack(self):
        print "Squeack!"

class FlyBehavior():
    def fly(self):
        pass

class Fly():


If you are going to defined FlyBehavior, you should really inherit from it. It just makes it a litle more clear what you are doing.

    def fly(self):
        print "I'm flying!"

class FlyNot():
    def fly(self):
        print "Can't fly..."

class Duck():


I'd define a constructor taking the quack and fly behavior here.

    def display(self):
        print this.name

    def performQuack(self):
        self.quackBehavior.quack()

    def performFly(self):
        self.flyBehavior.fly()

class MallardDuck(Duck):
    def __init__(self):
        self.quackBehavior = Quack()
        self.flyBehavior = Fly()


There's not really a reason for this to be a class. I'd make a function that sets up the Duck and returns it.    

if __name__ == "__main__":
    mallard = MallardDuck()
    mallard.performQuack()
    mallard.performFly()
    mallard.flyBehavior = FlyNot()
    mallard.performFly()