[Python-Dev] Re: decorators and 2.4

[Barry Warsaw]

On Mon, 2004-06-28 at 12:50, Jeff Bone wrote:
> > Just one more opinion here, but I'm with Bob on this one. Sure, many
> > of the uses I envision are "declarative" in the sense that they just
> > associate metadata with the function. But many other uses I envision
> > would alter the function's behavior.
> 
> I'm really curious what these uses might be.

Here's one of my use case.  

In the Mailman3 implementation of the BerkeleyDB backend storage, I need
to set up Berkeley transactions around various calls.  It's
programmatically possible to set up an explicit transaction to group
several operations together, but it's also possible to wrap a single
operation in a single transaction.  Also, the Berkeley transactions must
be wrapped in try/excepts so that if any Python level exception occurs,
the transaction can be properly aborted.

There's enough complexity in the implementation, and similarity in the
use, that I wanted to encapsulate all that in a 'txnprop' decorator.  I
currently use the 'call-after-def' wrapper idiom that's possible in
Python 2.3 today, but I want to use decorators for this, especially
because I sometimes want to combine the txnprop wrapper with other
decorators.

Here's a pointer to some of the code:

http://cvs.sourceforge.net/viewcvs.py/mailman/mailman3/src/mailman/berkeleydb/bdblist.py?rev=3.2&view=auto

The txnprop() descriptor guarantees that self.txn is bound to a
transaction inside the method call.

-Barry

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