code: def _datatable_factory(self):
          
          feed_cols = ['feed{0:03d}'.format(i + 1) for i in range(self.n_feeds)]
          feed_cols = ['override_feed000'] + feed_cols + ['failsafe_feed999']
  
          ind_sqlatyp = indexingtypes[self.index.indimp].sqlatyp
          dat_sqlatyp = datadefs[self.dtype.datadef].sqlatyp
  
          atbl = Table(self.name, Base.metadata,
                       Column('indx', ind_sqlatyp, primary_key=True),
                       Column('final', dat_sqlatyp),
                       *(Column(fed_col, dat_sqlatyp) for fed_col in feed_cols),
                       extend_existing=True)
          
          self.dt_feed_cols = feed_cols[:]
          self.dt_all_cols = ['indx', 'final'] + feed_cols[:]
          return atbl
docs: creates a SQLAlchemy Table object with the appropriate number of
          columns given the number of feeds