python 的with用途（清理资源和异常处理，同时代码精简）

#!/usr/bin/env python
# with_example02.py

class Sample:
def __enter__(self):
print "go to enter():"
return self

def __exit__(self, type, value, trace):
print "go to exit():"
print "type:", type
print "value:", value
print "trace:", trace

def do_something(self):
print "go to do_something():"
bar = 1/0
return bar + 10

with Sample() as sample:
sample.do_something()