code: def distinct_column_values_at_locus(
              self,
              column,
              feature,
              contig,
              position,
              end=None,
              strand=None):
          
          return self.column_values_at_locus(
              column,
              feature,
              contig,
              position,
              end=end,
              strand=strand,
              distinct=True,
              sorted=True)
docs: Gather all the distinct values for a property/column at some specified
          locus.
  
          Parameters
          ----------
          column : str
              Which property are we getting the values of.
  
          feature : str
              Which type of entry (e.g. transcript, exon, gene) is the property
              associated with?
  
          contig : str
              Chromosome or unplaced contig name
  
          position : int
              Chromosomal position
  
          end : int, optional
              End position of a range, if unspecified assume we're only looking
              at the single given position.
  
          strand : str, optional
              Either the positive ('+') or negative strand ('-'). If unspecified
              then check for values on either strand.