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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def create(cls, name, user=None, network_element=None, domain_name=None, zone=None, executable=None):
 """ Create a match expression :param str name: name of match expression :param str user: name of user or user group :param Element network_element: valid network element type, i.e. host, network, etc :param DomainName domain_name: domain name network element :param Zone zone: zone to use :param str executable: name of executable or group :raises ElementNotFound: specified object does not exist :return: instance with meta :rtype: MatchExpression """

        ref_list = []
        if user:
            pass
        if network_element:
            ref_list.append(network_element.href)
        if domain_name:
            ref_list.append(domain_name.href)
        if zone:
            ref_list.append(zone.href)
        if executable:
            pass

        json = {'name': name,
                'ref': ref_list}

        return ElementCreator(cls, json)