#!/usr/bin/python
#coding:utf8
#-------------------------------------------------------------------------------
# Name:        python中异常的处理与跑抛出
# Author:      quan
# Created:     21/09/2013
#-------------------------------------------------------------------------------


#python中的with的使用，

"""
python中with可以明显改进代码友好度，比如：
[python] view plaincopyprint?
with open('a.txt') as f:
    print f.readlines()

为了我们自己的类也可以使用with， 只要给这个类增加两个函数__enter__, __exit__即可：
[python] view plaincopyprint?
>>> class A:
    def __enter__(self):
        print 'in enter'
    def __exit__(self, e_t, e_v, t_b):
        print 'in exit'

>>> with A() as a:
    print 'in with'

in enter
in with
in exit

另外python库中还有一个模块contextlib，使你不用构造含有__enter__, __exit__的类就可以使用with：
[python] view plaincopyprint?
>>> from contextlib import contextmanager
>>> from __future__ import with_statement
>>> @contextmanager
... def context():
...     print 'entering the zone'
...     try:
...         yield
...     except Exception, e:
...         print 'with an error %s'%e
...         raise e
...     else:
...         print 'with no error'
...
>>> with context():
...     print '----in context call------'
...
entering the zone
----in context call------
with no error

使用的最多的就是这个contextmanager, 另外还有一个closing 用处不大
[python] view plaincopyprint?
from contextlib import closing
import urllib

with closing(urllib.urlopen('http://www.python.org')) as page:
    for line in page:
        print line
"""
#自己写的事例
#首先定义一个类

class with_python():
    #初始化一个数组的，类型行
    def __init__(self,list_name):
        self.list = list_name

    #定义with调用函数（使用with必有得选项）
    def __enter__(self):
        self.aa = self.list
        return self.aa
    #退出选项 （使用with必有得选项）
    def __exit__(self,type,value,tb):
        if type == None:
            self.list = self.aa
        return False


item = [1,2,]

#进行上下为管理
with with_python(item) as  list_one:
    list_one.append(1)
    list_one.append(3)
    list_one.pop(0)
    print list_one

print item