类和对象是面向对象编程的两个方面。
类的方法和普通函数只有一个区别，他们必须有一个额外的参数，在调用这个方法时不需要为这个参数赋值，python为自动为其赋值，这个变量就是self
举个例子
有一个类叫做MyClass,一个类对象叫做MyObject
调用myclass的方法method
MyObject.method(arg1, arg2)
python会自动转换成
MyClass.method(MyObject, arg1, arg2)
#!/usr/bin/python #filename: simpleclass.py class Person: #this is an empty block pass p = Person() print p
$ python simpleclass.py <__main__.Person instance at 0x7f810657eef0>
这里就在Person类中定义的方法sayHi增加了一个self参数
#!/usr/bin/python #filename: method.py class Person: def sayHi(self): print 'Hello,how are you?' p = Person() p.sayHi() #also can be written like this Person().sayHi()
$ python method.py Hello,how are you? Hello,how are you?
__init__方法在类的一个对象被建立时，马上运行。这个方法可以用来对你的对象做一些你希望的 初始化 。注意，这个名称的开始和结尾都是双下划线。
#!/usr/bin/python
class Person:
def __init__(self,name):
self.name = name
def sayHi(self):
print 'Hello, my name is',self.name
p = Person('John')
p.sayHi()
#this also can be written like this
Person('John').sayHi()$ python class_init.py Hello, my name is John Hello, my name is John
类变量和对象变量
#!/usr/bin/python
# filename: objvar.py
class Person:
population = 0
def __init__(self,name):
self.name = name
print '(Initializing %s)' % self.name
Person.population += 1
def __del__(self):
print '%s says bye.' % self.name
Person.population -= 1
if Person.population == 0:
print 'I am the last one.'
else:
print 'There are still %d people left.' %Person.population
def sayHi(self):
print 'Hi, my name is %s.' % self.name
def howMany(self):
if Person.population == 1:
print 'I am the only person here.'
else:
print 'We have %s people here' % Person.population
swaroop = Person('Swaroop')
swaroop.sayHi()
swaroop.howMany()
kalam = Person('Abdul Kalam')
kalam.sayHi()
kalam.howMany()
swaroop.sayHi()
swaroop.howMany()$ python objvar.py (Initializing Swaroop) Hi, my name is Swaroop. I am the only person here. (Initializing Abdul Kalam) Hi, my name is Abdul Kalam. We have 2 people here Hi, my name is Swaroop. We have 2 people here Abdul Kalam says bye. There are still 1 people left. Swaroop says bye. I am the last one.
观察可以发现__init__方法用一个名字来初始化Person实例。在这个方法中，我们让population增加1，这是因为我们增加了一个人。同样可以发现，self.name的值根据每个对象指定，这表明了它作为对象的变量的本质。
记住，你只能使用self变量来参考同一个对象的变量和方法。这被称为 属性参考 。
在这个程序中，我们还看到docstring对于类和方法同样有用。我们可以在运行时使用Person.__doc__和Person.sayHi.__doc__来分别访问类与方法的文档字符串。
就如同__init__方法一样，还有一个特殊的方法__del__，它在对象消逝的时候被调用。对象消逝即对象不再被使用，它所占用的内存将返回给系统作它用。在这个方法里面，我们只是简单地把Person.population减1。
当对象不再被使用时，__del__方法运行，但是很难保证这个方法究竟在 什么时候 运行。如果你想要指明它的运行，你就得使用del语句，就如同我们在以前的例子中使用的那样。
继承就是为了实现代码的重用
#!/usr/bin/python
#filename: inherit.py
class SchoolMember:
def __init__(self,name,age):
self.name = name
self.age = age
print '(Initialized SchoolMember: %s)' % self.name
def tell(self):
print 'Name:"%s" Age:"%s"' % (self.name,self.age),
class Teacher(SchoolMember):
def __init__(self,name,age,salary):
SchoolMember.__init__(self,name,age)
self.salary = salary
print '(Initialized Teacher: %s)' % self.name
def tell(self):
SchoolMember.tell(self)
print 'Salary: "%d"' % self.salary
class Student(SchoolMember):
def __init__(self,name,age,marks):
SchoolMember.__init__(self,name,age)
self.marks = marks
print '(Initialized Student: %s)' % self.name
def tell(self):
SchoolMember.tell(self)
print 'Marks: "%d" ' %self.marks
t = Teacher('Mrs. Shrividya',40,30000)
s = Student('Swaroop', 22, 75)
print
members = [t, s]
for member in members:
member.tell()$ python inherit.py (Initialized SchoolMember: Mrs. Shrividya) (Initialized Teacher: Mrs. Shrividya) (Initialized SchoolMember: Swaroop) (Initialized Student: Swaroop) Name:"Mrs. Shrividya" Age:"40" Salary: "30000" Name:"Swaroop" Age:"22" Marks: "75"
参考文档：
http://woodpecker.org.cn/abyteofpython_cn/chinese/ch11.html#s01
