code: def _is_small_vcf(vcf_file):
      
      count = 0
      small_thresh = 250
      with utils.open_gzipsafe(vcf_file) as in_handle:
          for line in in_handle:
              if not line.startswith("#"):
                  count += 1
              if count > small_thresh:
                  return False
      return True
docs: Check for small VCFs which we want to analyze quicker.