<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def port_create_vlan(br, port, id, internal=False):
    '''
    Isolate VM traffic using VLANs.

    Args:
        br: A string - bridge name.
        port: A string - port name.
        id: An integer in the valid range 0 to 4095 (inclusive), name of VLAN.
        internal: A boolean to create an internal interface if one does not exist.

    Returns:
        True on success, else False.

    .. versionadded:: 2016.3.0

    CLI Example:
    .. code-block:: bash

       salt '*' openvswitch.port_create_vlan br0 tap0 100
    '''
    interfaces = __salt__['network.interfaces']()
    if not 0 <= id <= 4095:
        return False
    elif not bridge_exists(br):
        return False
    elif not internal and port not in interfaces:
        return False
    elif port in port_list(br):
        cmd = 'ovs-vsctl set port {0} tag={1}'.format(port, id)
        if internal:
            cmd += ' -- set interface {0} type=internal'.format(port)
        result = __salt__['cmd.run_all'](cmd)
        return _retcode_to_bool(result['retcode'])
    else:
        cmd = 'ovs-vsctl add-port {0} {1} tag={2}'.format(br, port, id)
        if internal:
            cmd += ' -- set interface {0} type=internal'.format(port)
        result = __salt__['cmd.run_all'](cmd)
        return _retcode_to_bool(result['retcode'])