docs: def set_timezone(new_tz=None):
      """Set the timezone for datetime fields.
      By default is your machine's time.
      If it's called without parameter sets the
      local time again.
  
      :keyword param new_tz: timezone string
      ex. 'Europe/Athens',
          'Asia/Seoul',
          'America/Los_Angeles',
          'UTC'
  
      :return
          None
      """
      global tz
      if new_tz:
          tz = pytz.timezone(new_tz)
      else:
          tz = tzlocal.get_localzone()