python有自动资源管理吗？

Question

All versions of Java require the user to close resources manually - usually handled in the finally block. Java 7 is about to get ARM (automatic resource management) blocks.

1. Firstly I don't see a finally block concept in python. Or do you close resources in the catch for each raised exceptions ?
2. Is there a library that performs ARM in python ? If not, then what is the pythonic way to do ARM ?

Answer 1

There is a try: except: finally: in python.

You can also use the with: statement, which I believe is what you are after for ARM. These are called context managers. http://www.python.org/dev/peps/pep-0343/

Answer 2

There is some automated resource management in Python. Most objects who open resources will close them when they get garbage collected. When that happens is undefined, and it may not happen at all, so this only works if you don't use very many resources, don't care if they are open long and the resources will be closed by the operating system when the program exits.

Otherwise, use context managers and the with statement as per Matthews answer.

Here is a simple example that redirects stdout:

>>> import sys
>>> class redirect_stdout:
...     def __init__(self, target):
...         self.stdout = sys.stdout
...         self.target = target
...
...     def __enter__(self):
...         sys.stdout = self.target
...
...     def __exit__(self, type, value, tb):
...         sys.stdout = self.stdout
...
>>> from StringIO import StringIO
>>> out = StringIO()
>>> with redirect_stdout(out):
...     print 'Test'
...
>>> out.getvalue() == 'Test\n'
True