#!/usr/bin/env python
# -*- coding: utf-8 -*-# a class definition
class MyClass:"""一个简单的类定义 A Simple Example Class"""i = 1234  #类的成员变量 def f(self):#类的成员函数return "Hello World"x = MyClass()
print MyClass.__doc__
print x.__doc__#显示定义一个类的初始化方法
class Complex:def __init__(self, realpart, imagpart):self.r = realpartself.i = imagpartx = Complex(3.0, -4.5)
print x.r, x.i
x.counter = 2 #instance attribute
print x.counter # print Complex.counter将出错
del x.counter#类的成员函数也可以在外部定义
def f1(self, x, y):return min(x, x+y)class C:f = f1def g(self):return 'hello world'h = g
#这样C.f C.h C.g都是合法的函数对象#在类的函数定义中，可以使用self引用类的其他成员变量或函数对象
class Bag:def __init__(self):self.data = []def add(self, x):self.data.append(x)def addtwice(self, x):self.add(x)self.add(x)#继承与多重继承
class BaseClassName:passclass DerivedClass(BaseClassName):passclass BaseClassName2:passclass DerivedClass2(BaseClassName, BaseClassName2):pass#实用方法isintance issubclass
d = DerivedClass2()
print isinstance(d, BaseClassName)
print issubclass(DerivedClass2, BaseClassName2)#私有变量
#在python中，没有真正意义上的私有概念，一般约定命名中以下划线开头的变量或函数为私有的。
class Mapping:def __init__(self, iterable):self.items_list = []self.__update(iterable)def update(self, iterable):for item in iterable:self.items_list.append(item)__update = update   # private copy of original update() methodclass MappingSubclass(Mapping):def update(self, keys, values):# provides new signature for update()# but does not break __init__()for item in zip(keys, values):self.items_list.append(item)#类似C中的结构体的使用
class Employee:passjohn = Employee() # Create an empty employee record# Fill the fields of the record
john.name = 'John Doe'
john.dept = 'computer lab'
john.salary = 1000#在python中，用户自定义的异常也被认为是类
#有两种形式raise Class, instance 和 raise instance
class B:pass
class C(B):pass
class D(C):passfor c in [B, C, D]:try:raise c()except D:print "D"except C:print "C"except B:print "B"#迭代器的实现
class Reverse:"""Iterator for looping over a sequence backwards."""def __init__(self, data):self.data = dataself.index = len(data)def __iter__(self):return selfdef next(self):if self.index == 0:raise StopIterationself.index = self.index - 1return self.data[self.index]rev = Reverse('spam')
for char in rev:print char#产生器
def reverse(data):for index in range(len(data)-1, -1, -1):yield data[index]for char in reverse('golf'):print char