docs: def dt2ts(dt):
      """Converts to float representing number of seconds since 1970-01-01 GMT."""
      # Note: no assertion to really keep this fast
      assert isinstance(dt, (datetime.datetime, datetime.date))
      ret = time.mktime(dt.timetuple())
      if isinstance(dt, datetime.datetime):
          ret += 1e-6 * dt.microsecond
      return ret