Currently, if I want to copy a table while adding a few columns (as specified by schema in the example) I need to do something like:

        cat = afwTable.SourceCatalog(schema)

        cat.table.defineCentroid(srcCat.table.getCentroidDefinition())

        cat.table.definePsfFlux(srcCat.table.getPsfFluxDefinition())

        # etc.

        scm = afwTable.SchemaMapper(srcCat.getSchema(), schema)

        for schEl in srcCat.getSchema():

            scm.addMapping(schEl.getKey(), True)

        cat.extend(srcCat, True, scm)

Please make this easier! For example

• by adding a flag to the SchemaMapper constructor that automatically does the addMapping (should this be the default?)
• by making it possible to copy all the slots (maybe this'll be the case when the new alias scheme is implemented?).

Maybe we just need a new method:

cat = srcCat.extend(schema)

that does all the above steps.