On 01/25/10 05:51 PM, [email protected] wrote:
On Mon, Jan 25, 2010 at 05:34:06PM -0600, Shawn Walker wrote:
There's one more option. We can require callers to call the new
generator close method on the returned generator object (the value
returned by a generator initially) and then rely on the finally
cause for cleanup:
Thanks. I did see that once I was able to read the documentation. I
was initially put off on that idea because the itertools functions don't
invoke a generator's close function. The itertools package assumes that
all objects are only iterable and just have a next() method.
This is actually the officially endorsed method as noted via pep 325,
and its replacement (pep 342). So there's a formal mechanism in place here.
Brock observed that as long as we make the calling convention
explicit, we can probably get away with using close() instead of a more
complicated approach. The existing callers of remote_search() chain the
results and iterate through all of them. This will work by default.
It's only if we get a fancy caller of remote_search() that we'll need to
worry about the locking issues. If we force those callers to close each
generator before invoking the next, then that should be sufficient.
They don't have to explicitly call close() if the generator itself
returns control. Only if they wish to abort generator execution.
Calling close() on the generator actually will throw() a GeneratorExit
exception that the generator can call for the forced abort case.
However, since we actually want the same thing to happen for a clean
finish as for an aborted, relying on finally: seems reasonable.
Since you and Brock seem to be in agreement about this approach, I'll
pull the existing locking out of remote search and put it in a
generator of a generator wrapper that we discussed earlier. I hope to
have a new webrev for that out before too long.
Thanks to both you and Brock for being patient while I got my head
around all of the issues here.
I actually wasn't aware of some of the try/finally pitfalls with
generators until today. It's worth noting that python2.4 doesn't allow
a yield statement in a try/finally block, and that there have been
significant improvements in python2.5 and python2.6 for generators.
Cheers,
--
Shawn Walker
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