Understanding Python's "with" statement
基本構文
class controlled_execution:
def __enter__(self):
set things up
return thing
def __exit__(self, type, value, traceback):
tear things down
with controlled_execution() as thing:
some code
__exit__内で true value を返すと例外を投げるようです。
例えば、 return isinstance(value, TypeError) のように。
PEP 0343
The with statement (2.6リファレンス)
