2012/4/5 Peter Eisentraut <pete...@gmx.net> > On lör, 2012-03-24 at 16:24 -0400, Tom Lane wrote: > > Peter Eisentraut <pete...@gmx.net> writes: > > > On ons, 2012-03-07 at 17:14 -0500, Tom Lane wrote: > > >> I said it was a reasonable alternative, not that it was the only one > > >> we should consider. The behavior of .nrows() might be accidental, > > >> but perhaps it is a preferable model to adopt. > > > > > After pondering this for several days now I still think the best > > > approach is to change .nrows() to return None for utility commands and > > > have the other metadata functions throw exceptions. > > > > OK, I don't have strong feelings about it. > > Well, scratch that. > > This whole area is sloppily documented. resultset.nrows() returns > SPI_processed, which is the number of rows, er, processed by the > statement, which may or may not be the number of rows returned. So a > statement that returns no result set could very well have nrows() > 0. > > The number of rows returned can be obtained by using len(resultset) (not > documented, but one could perhaps guess it). But len() cannot return > None, so we cannot use that as a marker. > > The alternatives are now to introduce a new function like has_rows() > that returns True iff result rows exist and therefore result metadata > can be fetched, or go back to having coltypes() et al. return None when > no metadata exists. I'm in favor of the latter, because the former > would add somewhat needless complications and doesn't really add any > robustness or the like. >
I consider that this is an error to request metadata when the query does not return some. For example: "UPDATE mytable SET value = 1" does not return column metadata, so user is not supposed to col coltypes(). That's why I propose to return an error. coltypes() is supposed to return a sequence, not None. Checking for None is a bad coding practise IMO, especially when dealing with lists. But anyway, returning None or raising an error is still much better than crashing :-) Cheers, -- Jean-Baptiste Quenot
