a Python dictionary with all the set operators

dictpp.py

#!/usr/bin/env python -O
#
# Copyright (c) 2013 Kyle Gorman
#
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# copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
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# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be included
# in all copies or substantial portions of the Software.
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
# OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
#
# dictpp.py: adding set operations (and semantics) to dictionaries
# Kyle Gorman <gormanky@ohsu.edu>


class DictPP(dict):

    """
    A Python dictionary, now with set operations. These operate on keys,
    rather than on key-value pairs (as you might expect) as there is no
    reason to assume that a value will be immutable/hashable.
    """

    def isdisjoint(self, other):
        """
        True iff self and other share no keys

        >>> x = DictPP({'spam': 5, 'eggs': 3})
        >>> y = DictPP({'liver': 2})
        >>> z = DictPP({'spam': 2})
        >>> x.isdisjoint(y)
        True
        >>> x.isdisjoint(z)
        False
        """
        return set(self).isdisjoint(other)

    # no need to implement issubset (<=) or issuperset (>=); base
    # dictionaries already have those methods

    def __sub__(self, other):
        """
        Difference: items in self whose keys are not in other

        >>> x = DictPP({'spam': 5, 'eggs': 3})
        >>> y = DictPP({'liver': 2})
        >>> z = DictPP({'spam': 2})
        >>> (x - y) == x
        True
        >>> sorted((x - z).keys())
        ['eggs']
        >>> sorted((x - x).keys())
        []
        """
        return {k: v for (k, v) in self.iteritems() if k not in other}

    def difference(self, other):
        return self - other

    def __isub__(self, other):
        return self - other

    def difference_update(self, other):
        self -= other

    def __xor__(self, other):
        """
        Symmetric difference: items in self whose keys are not in other,
        or items in other whose keys are not in self

        >>> x = DictPP({'spam': 5, 'eggs': 3})
        >>> y = DictPP({'liver': 2})
        >>> z = DictPP({'spam': 2})
        >>> sorted((x ^ y).keys())
        ['eggs', 'liver', 'spam']
        >>> sorted((x ^ z).keys())
        ['eggs']
        """
        return DictPP(self - other) | DictPP(other - self)

    def symmetric_difference(self, other):
        return self ^ other

    def __ixor__(self, other):
        return self ^ other

    def symmetric_difference_update(self, other):
        self ^= other

    def __and__(self, other):
        """
        Intersection: items in self whose keys are also in other 

        >>> x = DictPP({'spam': 5, 'eggs': 3})
        >>> y = DictPP({'liver': 2})
        >>> z = DictPP({'spam': 2})
        >>> sorted((x & y).keys())
        []
        >>> sorted((x & z).keys())
        ['spam']
        """
        return {k: v for (k, v) in self.iteritems() if k in other}

    def intersection(self, other):
        return self & other

    def __iand__(self, other):
        return self & other

    def intersection_update(self, other):
        self &= other

    def __or__(self, other):
        """
        Union: items in self and items in other

        >>> x = DictPP({'spam': 5, 'eggs': 3})
        >>> y = DictPP({'liver': 2})
        >>> z = DictPP({'spam': 2})
        >>> sorted((x | y).keys())
        ['eggs', 'liver', 'spam']
        >>> sorted((x | z).keys())
        ['eggs', 'spam']
        """
        return dict(self, **other)

    def union(self, other):
        return self | other

    def __ior__(self, other):
        return self | other

    # note that update does not need to be implemented; it already exists
    # in normal dictionaries

if __name__ == '__main__':
    import doctest
    doctest.testmod()