code: def query_position(self, chrom=None, position=None):
          
  
          if self.index is None:
              raise ValueError('no index has been set')
          if isinstance(self.index, SortedIndex):
              # ignore chrom
              loc = self.index.locate_key(position)
          else:
              loc = self.index.locate_key(chrom, position)
          return self[loc]
docs: Query the table, returning row or rows matching the given genomic
          position.
  
          Parameters
          ----------
          chrom : string, optional
              Chromosome/contig.
          position : int, optional
              Position (1-based).
  
          Returns
          -------
          result : row or VariantTable