chapter01_strategy

Chapter 1: Strategy design pattern

Strategy: defines a family of algorithms, encapsulates each one and makes them interchangeable. Strategy lets the algorithm vary independently of clients that use it.

Class Diagram

classDiagram
Client "1" --> "1" Strategy
Strategy "1" <|.. "*" ConcreteStrategyA
Strategy "1" <|.. "*" ConcreteStrategyB
    class Client {
        Strategy strategyBehavior
    inheritedMethod()
    }
    class Strategy {
    <<interface>> 
    strategyBehaviorMethod()}

    class ConcreteStrategyA {
    strategyBehaviorMethod() 
    }
    class ConcreteStrategyB {
    strategyBehaviorMethod() 
    }

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Use in Python

The more pythonic approach in my mind is to define methods within an appropriate namespace rather than classes; this does not violate the above definition. The class-based approach is needed in Java and has the advantage of explicitly setting out the required method in an abstract base class.

An example from the standard lib is changing the text completion method from the readline module. This is used by the python REPL when we hit TAB in the REPL. We can change the completion behavior via the set_completer() method, which takes a function which replaces the current completion function. The function is used explicitly to set the required behavior.