software development traditional software development involves several phases three major steps are design implementation testing and debugging in this sectionwe briefly discuss the role of these phasesand we introduce several good practices for programming in pythonincluding coding stylenaming conventionsformal documentationand unit testing design for object-oriented programmingthe design step is perhaps the most important phase in the process of developing software for it is in the design step that we decide how to divide the workings of our program into classeswe decide how these classes will interactwhat data each will storeand what actions each will perform indeedone of the main challenges that beginning programmers face is deciding what classes to define to do the work of their program while general prescriptions are hard to come bythere are some rules of thumb that we can apply when determining how to design our classesresponsibilitiesdivide the work into different actorseach with different responsibility try to describe responsibilities using action verbs these actors will form the classes for the program independencedefine the work for each class to be as independent from other classes as possible subdivide responsibilities between classes so that each class has autonomy over some aspect of the program give data (as instance variablesto the class that has jurisdiction over the actions that require access to this data behaviorsdefine the behaviors for each class carefully and preciselyso that the consequences of each action performed by class will be well understood by other classes that interact with it these behaviors will define the methods that this class performsand the set of behaviors for class are the interface to the classas these form the means for other pieces of code to interact with objects from the class defining the classestogether with their instance variables and methodsare key to the design of an object-oriented program good programmer will naturally develop greater skill in performing these tasks over timeas experience teaches him or her to notice patterns in the requirements of program that match patterns that he or she has seen before