python学习--动态类型

#-*- coding:utf-8 -*-
'''
Created on 2010-8-27
@author: qichen
'''
import sys
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# Python中的动态类介绍：
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# 1.类型属于对象，而不是变量
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a = 3                       
a = 'string'
a = 1.23
print type(a)                                        #<type 'float'>
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# 2.关于资源的回收 sys.getrefcount(3) 查询系统中，引用3个总和
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print sys.getrefcount(3)                             #38(不同机器运行状况不同)
a = 3
b = 3
print sys.getrefcount(3)                             #40
b = 4
print sys.getrefcount(3)                             #39
#===============================================================================
# 3.共享引用    同JAVA一样，String是不能改变的，而列表时可以改变的。
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a = 'string'
b = a
b = b + '_type'
print 'b is %s and a is %s' % (b , a)                #b is string and a is string_type
a = [0 , 1 , 2]
b = a
b[0] = 1
print 'b is %s and a is %s' % (b , a)                #b is [1, 1, 2] and a is [1, 1, 2]
a = [0 , 1 , 2]
b = [0 , 1 , 2]
print 'a and b is same values ? %s' % (a == b)       #True
print 'a and b is same object ? %s' % (a is b)       #False