code: def datetime_string(time_zone=False):
      
      time = datetime.datetime.now()
      template = u"%04d-%02d-%02dT%02d:%02d:%02d"
      if time_zone:
          template += u"+00:00"
      return template % (
          time.year,
          time.month,
          time.day,
          time.hour,
          time.minute,
          time.second
      )
docs: Return a string representing the current date and time,
      in ``YYYY-MM-DDThh:mm:ss`` or ``YYYY-MM-DDThh:mm:ss+hh:mm`` format
  
      :param boolean time_zone: if ``True``, add the time zone offset.
  
      :rtype: string