from datetime import datetime


def _date_to_ISO(strdate):
    """
    Return date in ISO format, from pyshark date output

    :type strdate: string of date (pyshark's output) that is not in ISO format
    :return: an ISO formatted date
    """
    return datetime.strptime(strdate, '%a, %d %b %Y %H:%M:%S %Z').isoformat()