Dict wrapper that tracks changes

diff.py

try:
    import cPickle as pickle
except ImportError:
    import pickle

class Dict(dict):
    """
    Dict that tracks changes. Changes = (New, Changed, Removed)
    """
    def __init__(s, *args, **kwargs):
        dict.__init__(s, *args, **kwargs)
        s._diff = {}; s.diff
    def diff():
        def fget(s):
            diff1 = set(dict.keys(s)) # Current keys
            diff2 = set(s._diff.keys()) # Old keys
            diff3 = dict((a, pickle.dumps(b, -1)) for a, b in dict.items(s)) # Changes
            new = diff1 - diff2 # New keys
            rem = diff2 - diff1 # Removed keys
            chg = set(a for a, b in diff3.items() if a in s._diff and a not in new and a not in rem and b != s._diff[a])
            s._diff = diff3
            return (new, chg, rem) if new or chg or rem else None
        def fset(s, v):
            if v:
                s._diff = {}
            else:
                s.diff
        return locals()
    diff = property(**diff())