python学习笔记三（类自定义属性 方法）

wskickahn

#encoding=UTF-8
'''
Created on 2011-5-26
@author: Administrator
'''
#静态变量
class A:
count=0
def __init__(self):
self.__class__.count+=1 #把它当全局变量来用
print A.count
a=A()
print a.count
b=A()
print b.count
# __str__ 和 __repr__ 和  __del__ 和 __eval__
class B:
def __repr__(self):
return "A()"
def __str__(self):
return "OK,I am in the class"
x=B()
print a
print x #结果被__str__重写了
print repr(x) #repr函数用来取得对象的规范字符串表示。重写__repr__
print eval("A()")
'''
0
1
2
<__main__.A instance at 0x01AEE828>
OK,I am in the class
A()
<__main__.A instance at 0x01AEEB20>
'''
# __cmp__的用法
class C:
def __cmp__(self,other):
if other>=0:return -1
elif other<0: return 1
else: return 0
c = C()
print c>-2  #true
print c>2  #false

# __nozero__ 用法
class Dog:
alive = 0
def __nonzero__(self):
if self.alive==0:return 0
else: return 1;
def isDogAlive(d):
if d:print "Alive"
else :print"Dead"
d = Dog()
print d.alive #0
isDogAlive(d)  #Dead
d.alive = 3
isDogAlive(d) #Alive
##########################
#__len__
class D:
def __len__(self):
return 100
d = D()
print len(d) #100