《python 从入门到精通》§7 更多抽象：对象

 

§7 更多抽象：对象

§7.1  对象的作用

多态、封装、继承

多态：

# Don't do it like this...

def getPrice(object):

if isinstance(object, tuple):

return object[1]

else:

return magic_network_method(object)

 

 

 

§7.2 类及类型

__metaclass__ = type # Make sure we get new style classes

class Person:

def setName(self, name):

self.name = name

def getName(self):

return self.name

def greet(self):

print "Hello, world! I'm %s." % self.nam

 

       __metaclass__ = type表示使用新的类。使其作为一个新类的子类也可以做到这点。

      

       >>> class Class:

def method(self):

print 'I have a self!'

>>> def function():

print "I don't..."

>>> instance = Class()

>>> instance.method()

I have a self!

>>> instance.method = function

>>> instance.method()

I don't...

 

python间接支持private，如下的__inaccessible即为私有的。

class Secretive:

def __inaccessible(self):

print "Bet you can't see me..."

def accessible(self):

print "The secret message is:"

self.__inaccessible()

 

但是依然可以这样访问：

>>> s._Secretive__inaccessible()

Bet you can't see me...

 

import * 不会导入下划线开头的方法。

 

指定父类：

 

class Filter:

def init(self):

self.blocked = []

def filter(self, sequence):

return [x for x in sequence if x not in self.blocked]

class SPAMFilter(Filter): # SPAMFilter is a subclass of Filter

def init(self): # Overrides init method from Filter superclass

self.blocked = ['SPAM']

 

>>> s = SPAMFilter()

>>> s.init()

>>> s.filter(['SPAM', 'SPAM', 'SPAM', 'SPAM', 'eggs', 'bacon', 'SPAM'])

['eggs', 'bacon']

 

>>> issubclass(SPAMFilter, Filter)

True

 

>>> SPAMFilter.__bases__

(,)

>>> Filter.__bases__

()

 

>>> s = SPAMFilter()

>>> isinstance(s, SPAMFilter)

True

>>> isinstance(s, Filter)

True

>>> isinstance(s, str)

False

       isinstance往往不如多态可靠。

      

多继承：

       class Calculator:

def calculate(self, expression):

self.value = eval(expression)

class Talker:

def talk(self):

print 'Hi, my value is', self.value

class TalkingCalculator(Calculator, Talker):

pass

       如果方法相同，前面一个父类重载后面父类的。

      

       检查属性是否存在

       >>> hasattr(tc, 'talk')

True

>>> hasattr(tc, 'fnord')

False

       检查函数是否可以调用：

       >>> callable(getattr(tc, 'talk', None))

True

       callable在3.0要使用：hasattr(x, '__call__').

      

       修改属性：

       >>> setattr(tc, 'name', 'Mr. Gumby')

>>> tc.name

'Mr. Gumby

       查看一个对象中的所有属性：__dict__。inspect模块可以查看一个对象的组成。

 

§7.3 面向对象设计

略