code: def _find_bgzip():
      
      missing_file_exception = OSError if six.PY2 else FileNotFoundError
      min_bgzip_version = ".".join(map(str, min_bgzip_version_info))
      exe = os.environ.get("SEQREPO_BGZIP_PATH", which("bgzip") or "/usr/bin/bgzip")
  
      try:
          bgzip_version = _get_bgzip_version(exe)
      except AttributeError:
          raise RuntimeError("Didn't find version string in bgzip executable ({exe})".format(exe=exe))
      except missing_file_exception:
          raise RuntimeError("{exe} doesn't exist; you need to install htslib (See https://github.com/biocommons/biocommons.seqrepo#requirements)".format(exe=exe))
      except Exception:
          raise RuntimeError("Unknown error while executing {exe}".format(exe=exe))
      bgzip_version_info = tuple(map(int, bgzip_version.split(".")))
      if bgzip_version_info < min_bgzip_version_info:
          raise RuntimeError("bgzip ({exe}) {ev} is too old; >= {rv} is required; please upgrade".format(
              exe=exe, ev=bgzip_version, rv=min_bgzip_version))
      logger.info("Using bgzip {ev} ({exe})".format(ev=bgzip_version, exe=exe))
      return exe
docs: return path to bgzip if found and meets version requirements, else exception