def dict_diff(prv, nxt):
    """Return a dict of keys that differ with another config object."""
    keys = set(prv.keys() + nxt.keys())
    result = {}
    for k in keys:
        if prv.get(k) != nxt.get(k):
            result[k] = prv.get(k), nxt.get(k)
    return result
