def canonical_interface_name(interface, addl_name_map=None):
    """Function to return an interface's canonical name (fully expanded name).

    Use of explicit matches used to indicate a clear understanding on any potential
    match. Regex and other looser matching methods were not implmented to avoid false
    positive matches. As an example, it would make sense to do "[P|p][O|o]" which would
    incorrectly match PO = POS and Po = Port-channel, leading to a false positive, not
    easily troubleshot, found, or known.

    :param interface: The interface you are attempting to expand.
    :param addl_name_map (optional): A dict containing key/value pairs that updates
    the base mapping. Used if an OS has specific differences. e.g. {"Po": "PortChannel"} vs
    {"Po": "Port-Channel"}
    """

    name_map = {}
    name_map.update(base_interfaces)
    interface_type, interface_number = split_interface(interface)

    if isinstance(addl_name_map, dict):
        name_map.update(addl_name_map)
    # check in dict for mapping
    if name_map.get(interface_type):
        long_int = name_map.get(interface_type)
        return long_int + py23_compat.text_type(interface_number)
    # if nothing matched, return the original name
    else:
        return interface