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