def list_nics(nic_type=None):
    """Return a list of nics of given type(s)"""
    if isinstance(nic_type, six.string_types):
        int_types = [nic_type]
    else:
        int_types = nic_type

    interfaces = []
    if nic_type:
        for int_type in int_types:
            cmd = ['ip', 'addr', 'show', 'label', int_type + '*']
            ip_output = subprocess.check_output(cmd).decode('UTF-8')
            ip_output = ip_output.split('\n')
            ip_output = (line for line in ip_output if line)
            for line in ip_output:
                if line.split()[1].startswith(int_type):
                    matched = re.search('.*: (' + int_type +
                                        r'[0-9]+\.[0-9]+)@.*', line)
                    if matched:
                        iface = matched.groups()[0]
                    else:
                        iface = line.split()[1].replace(":", "")

                    if iface not in interfaces:
                        interfaces.append(iface)
    else:
        cmd = ['ip', 'a']
        ip_output = subprocess.check_output(cmd).decode('UTF-8').split('\n')
        ip_output = (line.strip() for line in ip_output if line)

        key = re.compile(r'^[0-9]+:\s+(.+):')
        for line in ip_output:
            matched = re.search(key, line)
            if matched:
                iface = matched.group(1)
                iface = iface.partition("@")[0]
                if iface not in interfaces:
                    interfaces.append(iface)

    return interfaces
Return a list of nics of given type(s)