def get_iana_tz(windows_tz):
timezone = WIN_TO_IANA.get(windows_tz)<EOL>if timezone is None:<EOL><INDENT>timezone = WIN_TO_IANA.get(windows_tz + '<STR_LIT>')<EOL><DEDENT>if timezone is None:<EOL><INDENT>raise pytz.UnknownTimeZoneError(<EOL>"<STR_LIT>" + windows_tz)<EOL><DEDENT>return timezone<EOL>
Returns a valid pytz TimeZone (Iana/Olson Timezones) from a given
    windows TimeZone

    :param windows_tz: windows format timezone usually returned by
     microsoft api response
    :return:
    :rtype: