PL/Python: Add cursor and execute methods to plan object

Something that has been bothering me in PL/Python for a long time is the
non-object-oriented way in which plans are prepared and executed:

plan = plpy.prepare(...)
res = plpy.execute(plan, ...)

where plpy.execute() takes either a plan or a query string.

I think a better style would be

plan = plpy.prepare(...)
res = plan.execute(...)

so that the "plan" is more like a statement handle that one finds in
other APIs.

This ended up being very easy to implement, so I'm proposing to allow
this new syntax as an alternative.

I came across this again as I was developing the background sessions API
for PL/Python. So I'm also wondering here which style people prefer so
I can implement it there.

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services