the formal ways you can move through collection of data items "the mediator pattern,takes up the important mediator pattern this pattern defines how communication between objects can be simplified by using separate object to keep all objects from having to know about each other "the memento pattern,saves the internal state of an objectso you can restore it later in "the observer pattern,we look at the observer patternwhich enables you to define the way number of objects can be notified of change in program state "the state pattern,describes the state patternwhich allows an object to modify its behavior when its internal state changes "the strategy pattern,describes the strategy patternwhichlike the state patternswitches easily between algorithms without any monolithic conditional statements the difference between the state and strategy patterns is that the user generally chooses which of several strategies to apply in "the template pattern,we look at the template pattern this pattern formalizes the idea of defining an algorithm in class but leaves some of the details to be implemented in subclasses in other wordsif your base class is an abstract classas often happens in these design patternsyou are using simple form of the template pattern "the visitor pattern,explores the visitor patternwhich turns the tables on the object-oriented model and creates an external class to act on data in other classes this is useful if there are fair number of instances of small number of classes and you want to perform some operation that involves all or most of them part " brief introduction to pythonin this last section of the bookwe provide succinct summary of the python language if you are only passingly familiar with pythonthis will get you up to speed it is sufficiently thorough to instruct beginner as well in "variables and syntax in python,we review the basic python variables and syntaxand in "making decisions in python,we illustrate the ways your programs can make decisions in "development environments,we provide short summary of the most common development environmentsand in "python collections and files,we discuss arrays and files finally in "functions,we take up how to use functions on python enjoy writing design patterns and learning the ins and outs of the powerful python language