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 ¢    # Copyright (C) 2003-2007, 2009-2011 Nominum, Inc.
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# Permission to use, copy, modify, and distribute this software and its
# documentation for any purpose with or without fee is hereby granted,
# provided that the above copyright notice and this permission notice
# appear in all copies.
#
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# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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"""A simple Set class."""

class Set(object):
    """A simple set class.

    Sets are not in Python until 2.3, and rdata are not immutable so
    we cannot use sets.Set anyway.  This class implements subset of
    the 2.3 Set interface using a list as the container.

    @ivar items: A list of the items which are in the set
    @type items: list"""

    __slots__ = ['items']

    def __init__(self, items=None):
        """Initialize the set.

        @param items: the initial set of items
        @type items: any iterable or None
        """

        self.items = []
        if not items is None:
            for item in items:
                self.add(item)

    def __repr__(self):
        return "dns.simpleset.Set(%s)" % repr(self.items)

    def add(self, item):
        """Add an item to the set."""
        if not item in self.items:
            self.items.append(item)

    def remove(self, item):
        """Remove an item from the set."""
        self.items.remove(item)

    def discard(self, item):
        """Remove an item from the set if present."""
        try:
            self.items.remove(item)
        except ValueError:
            pass

    def _clone(self):
        """Make a (shallow) copy of the set.

        There is a 'clone protocol' that subclasses of this class
        should use.  To make a copy, first call your super's _clone()
        method, and use the object returned as the new instance.  Then
        make shallow copies of the attributes defined in the subclass.

        This protocol allows us to write the set algorithms that
        return new instances (e.g. union) once, and keep using them in
        subclasses.
        """

        cls = self.__class__
        obj = cls.__new__(cls)
        obj.items = list(self.items)
        return obj

    def __copy__(self):
        """Make a (shallow) copy of the set."""
        return self._clone()

    def copy(self):
        """Make a (shallow) copy of the set."""
        return self._clone()

    def union_update(self, other):
        """Update the set, adding any elements from other which are not
        already in the set.
        @param other: the collection of items with which to update the set
        @type other: Set object
        """
        if not isinstance(other, Set):
            raise ValueError('other must be a Set instance')
        if self is other:
            return
        for item in other.items:
            self.add(item)

    def intersection_update(self, other):
        """Update the set, removing any elements from other which are not
        in both sets.
        @param other: the collection of items with which to update the set
        @type other: Set object
        """
        if not isinstance(other, Set):
            raise ValueError('other must be a Set instance')
        if self is other:
            return
        # we make a copy of the list so that we can remove items from
        # the list without breaking the iterator.
        for item in list(self.items):
            if item not in other.items:
                self.items.remove(item)

    def difference_update(self, other):
        """Update the set, removing any elements from other which are in
        the set.
        @param other: the collection of items with which to update t