dictdiff.py

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"""Enumerate the differences between two dictionaries.
"""
        
# stand-in for a missing value -- can't use None, since that might already
# be in the dictionary under inspection
class __MISSING_CLS(object):
    def __repr__(self):
        return "<MISSING>"

MISSING = __MISSING_CLS()


def dictdiff(dict1, dict2):
    """Given two dictionaries, return a list of 3-tuples:
    (key, dict1-value, dict2-value) for each key on which the
    dictionaries differ. The list is unsorted but a simple call to 
    sort() or sorted() will sort by key.
    
    If is key is missing from one dictionary, that value will be
    represented in the tuple with the MISSING object defined in this
    module.
    
    >>> len(dictdiff({}, {}))
    0
    >>> dictdiff(dict(a=1), {})
    [('a', 1, <MISSING>)]
    >>> dictdiff(dict(a=1, b=2), dict(a=1))
    [('b', 2, <MISSING>)]
    >>> dictdiff(dict(a=1, b=2), dict(a=1, b=3))
    [('b', 2, 3)]
    >>> sorted(dictdiff(dict(a=None), dict(b=None)))
    [('a', None, <MISSING>), ('b', <MISSING>, None)]
    >>> dictdiff(dict(a=None), {})
    [('a', None, <MISSING>)]
    >>> sorted(dictdiff(dict(z=26, y=25), dict(a=1, b=2)))
    [('a', <MISSING>, 1), ('b', <MISSING>, 2), ('y', 25, <MISSING>), ('z', 26, <MISSING>)]
    """
    allkeys = set(dict1).union(dict2)
    valcomps = [(key, dict1.get(key, MISSING), dict2.get(key, MISSING))
            for key in allkeys]
    diffs = [(key, lhs, rhs) for key, lhs, rhs in valcomps if not lhs == rhs]
    return diffs

# ------------------------------------------------------------
# fill in some missing names for running the doctests under Jython

try:
    set
except NameError:
    from sets import Set as set

try:
    sorted
except NameError:
    def sorted(lst):
        listcopy = lst[:]
        listcopy.sort()
        return listcopy

# ------------------------------------------------------------

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