Example of Python with usage

with in python can significantly improve code friendliness, such as:

with open('a.txt') as f:  

    print f.readlines()  

To use with for our own class, just add two functions to this class, s 7en__, s 8en__ :

>>> 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  

In addition, there is one module contextlib in python library, which allows you to use with without building classes with s 14en__, s 15en__ :

>>> 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  

This is the contextmanager that is used the most, and there is another closing that is not very useful

from contextlib import closing  

import urllib  

  

with closing(urllib.urlopen('http://www.python.org')) as page:  

    for line in page:  

        print line