part iii begins with short discussion of structural patterns "the adapter pattern,examines the adapter patternwhich is used to convert the programming interface of one class into that of another adapters are useful whenever you want unrelated classes to work together in single program "the bridge pattern,takes up the similar bridge patternwhich is designed to separate class' interface from its implementation this enables you to vary or replace the implementation without changing the client code "the composite pattern,delves into systems in which component may be an individual object or may represent collection of objects the composite pattern is designed to accommodate both casesoften in treelike structure in "the decorator pattern,we look at the decorator patternwhich provides way to modify the behavior of individual objects without having to create new derived class although this can apply to visual objects such as buttonsthe most common use in python is to create kind of macro that modifies the behavior of single class instance in "the facade pattern,we learn to use the facade pattern to write simplifying interface to code that otherwise might be unduly complex this deals with such an interface to couple of different databases "the flyweight pattern,describes the flyweight patternwhich enables you to reduce the number of objects by moving some of the data outside the class you can consider this approach when you have multiple instances of the same class "the proxy pattern,looks at the proxy patternwhich is used when you need to represent an object that is complex or time consuming to createby simpler one if creating an object is expensive in time or computer resourcesproxy enables you to postpone creation until you need the actual object "summary of structural patterns,summarizes these structural patterns part iv"behavioral patternspart iv outlines the behavioral patterns "chain of responsibility pattern,looks at how the chain of responsibility pattern allows decoupling between objects by passing request from one object to the next in chain until the request is recognized "the command pattern,shows how the command pattern uses simple objects to represent the execution of software commands additionallythis pattern enables you to support logging and undoable operations "the interpreter pattern,looks at the interpreter patternwhich provides definition of how to create little execution language and include it in program