code: def to_iso_date(date, default=None):
      
  
      # not a date
      if not is_date(date):
          return default
  
      # handle Zope DateTime objects
      if isinstance(date, (DateTime)):
          return date.ISO8601()
  
      # handle python datetime objects
      return date.isoformat()
docs: ISO representation for the date object
  
      :param date: A date object
      :type field: datetime/DateTime
      :returns: The ISO format of the date
      :rtype: str