#!/usr/bin/env python

# encoding: utf-8

#

# Copyright (c) 2010 Doug Hellmann. All rights reserved.

#

"""Implementing the context manager API by hand.

如果想啥文管理器可以处理这个异常

__exit__() 应当返回一个true值 来指示不需要传播这个异常

如果返回一个false 会导致__exit__()返回重新抛出这个异常

"""

#end_pymotw_header

class Context(object):

def __init__(self, handle_error):

print '__init__(%s)' % handle_error

self.handle_error = handle_error

def __enter__(self):

print '__enter__()'

return self

def __exit__(self, exc_type, exc_val, exc_tb):

print '__exit__()'

print ' exc_type =', exc_type

print ' exc_val =', exc_val

print ' exc_tb =', exc_tb

return self.handle_error

with Context(True):

raise RuntimeError('error message handled') #__exit__ 返回true 不抛出异常

print

with Context(False):

raise RuntimeError('error message propagated')#__exit__ 返回false抛出异常