diff_dict.py

class NotIn:
    def __repr__(self):
        return "<not in dict>"


NOT_IN = NotIn()


def ddiff(A, B):
    """ Create a dict that shows the difference between two dicts. """
    D = {}
    allkeys = set(A.keys() + B.keys())
    for k in allkeys:
        av, bv = A.get(k, NOT_IN), B.get(k, NOT_IN)
        if av != bv:
            D[k] = (av, bv)
    return D


def pprint_diff(A, B):
    """ Show the diff between two dict. """
    D = ddiff(A, B)
    added = {}
    removed = {}
    changed = {}
    for k, (av, bv) in D.items():
        if av == NOT_IN:
            added[k] = bv
        elif bv == NOT_IN:
            removed[k] = av
        else:
            changed[k] = (av, bv)
    print("{")
    for k in set(A.keys() + B.keys()):
        if k in added:
            print("  + {}: {},".format(k, added[k]))
        elif k in removed:
            print("  - {}: {},".format(k, removed[k]))
        elif k in changed:
            print("  ~ {}: {} -> {},".format(k, changed[k][0], changed[k][1]))
        else:
            print("    {}: {},".format(k, A[k]))
    print("}")


def main():
    A = dict(a=1, b=2, c=3)
    B = dict(a=1, b=3, d=4, e=None)
    D = ddiff(A, B)
    assert D == dict(b=(2, 3), c=(3, NOT_IN), d=(NOT_IN, 4), e=(NOT_IN, None))
    pprint_diff(A, B)


if __name__ == "__main__":
    main()