Python Programming On Win32

Classes

Python makes object-oriented programming easy. The class statement begins the definition of a class. Classes can use a special constructor called __init__( ) to initialize their data. Because Python doesn’t declare variables, this constructor is a common place to initialize any variables the class may require:

>>> class Car:
...     def __init__(self):
...         self.milespergallon = 25.0
...         self.travelled = 0
...         self.color = 'blue'
...         self.gas = 20
...     def drive(self, miles):
...         self.travelled = self.travelled + miles
...         self.gas = self.gas - (miles / self.milespergallon)
...     
>>> c = Car()
>>> c.drive(100)
>>> c.travelled
100
>>> c.gas
16.0
>>>

Note that you have to use the keyword self each time you access an attribute.

As with other languages, classes may inherit from a base class and be initialized with arguments supplied by the constructor. We won’t give any further examples at this point; you can see many classes throughout this book, and the syntax is self-evident if you are used to object-oriented programming.