code: def features(self, ignore_unknown=False):
          
          if not self.db:
              raise ValueError("Please attach a gffutils.FeatureDB")
          for i in self.data.index:
              try:
                  yield gffutils.helpers.asinterval(self.db[i])
              except gffutils.FeatureNotFoundError:
                  if ignore_unknown:
                      continue
                  else:
                      raise gffutils.FeatureNotFoundError('%s not found' % i)
docs: Generator of features.
  
          If a gffutils.FeatureDB is attached, returns a pybedtools.Interval for
          every feature in the dataframe's index.
  
          Parameters
          ----------
          ignore_unknown : bool
              If True, silently ignores features that are not found in the db.