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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 ordered_covering(routing_table, target_length, aliases=dict(), no_raise=False):
 """Reduce the size of a routing table by merging together entries where possible. .. warning:: The input routing table *must* also include entries which could be removed and replaced by default routing. .. warning:: It is assumed that the input routing table is not in any particular order and may be reordered into ascending order of generality (number of don't cares/Xs in the key-mask) without affecting routing correctness. It is also assumed that if this table is unordered it is at least orthogonal (i.e., there are no two entries which would match the same key) and reorderable. .. note:: If *all* the keys in the table are derived from a single instance of :py:class:`~rig.bitfield.BitField` then the table is guaranteed to be orthogonal and reorderable. .. note:: Use :py:meth:`~rig.routing_table.expand_entries` to generate an orthogonal table and receive warnings if the input table is not orthogonal. Parameters Routing entries to be merged. target_length : int or None Target length of the routing table; the minimisation procedure will halt once either this target is reached or no further minimisation is possible. If None then the table will be made as small as possible. Other Parameters Dictionary of which keys and masks in the routing table are combinations of other (now removed) keys and masks; this allows us to consider only the keys and masks the user actually cares about when determining if inserting a new entry will break the correctness of the table. This should be supplied when using this method to update an already minimised table. no_raise : bool If False (the default) then an error will be raised if the table cannot be minimised to be smaller than `target_length` and `target_length` is not None. If True then a table will be returned regardless of the size of the final table. Raises ------ MinimisationFailedError If the smallest table that can be produced is larger than `target_length` and `no_raise` is False. Returns ------- Reduced routing table entries. A new aliases dictionary. """

    # Copy the aliases dictionary
    aliases = dict(aliases)

    # Perform an initial sort of the routing table in order of increasing
    # generality.
    routing_table = sorted(
        routing_table,
        key=lambda entry: _get_generality(entry.key, entry.mask)
    )

    while target_length is None or len(routing_table) > target_length:
        # Get the best merge
        merge = _get_best_merge(routing_table, aliases)

        # If there is no merge then stop
        if merge.goodness <= 0:
            break

        # Otherwise apply the merge, this returns a new routing table and a new
        # aliases dictionary.
        routing_table, aliases = merge.apply(aliases)

    # If the table is still too big then raise an error
    if (not no_raise and
            target_length is not None and
            len(routing_table) > target_length):
        raise MinimisationFailedError(target_length, len(routing_table))

    # Return the finished routing table and aliases table
    return routing_table, aliases