Think Python - Denison University

Chapter 15Classes and objects15.1 User-definedtypesWe have used many of Python’s built-in types; now we are going to define a new type. As anexample, we willcreate atype calledPointthat represents apoint intwo-dimensional space.Inmathematicalnotation,pointsareoftenwritteninparentheseswithacommaseparatingthecoordinates.For example, (0,0) represents the origin, and (x,y) represents the point x units to the rightand yunits up fromthe origin.There areseveral ways we might represent points inPython:• We could storethecoordinates separately intwo variables,xandy.• We could storethecoordinates as elements inalistortuple.• We could create a new type torepresent points as objects.Creating a new type is (a little) more complicated than the other options, but it has advantages thatwillbe apparent soon.A user-defined type isalsocalled a class. A class definition looks likethis:class Point(object):"""represents a point in 2-D space"""This header indicates that the new class is a Point, which is a kind of object, which is a built-intype.The body is a docstring that explains what the class is for. You can define variables and functionsinsideaclass definition, but wewillget back tothat later.Defining aclass namedPointcreates aclass object.>>> print Point