A revision-enabled dict subclass, so your dicts don't forget their prior entries.

VersionedDict

class VersionedDict(dict):
    '''A dictionary sublcass that remembers all or a defined number of prior entries for a key.
    Allows reversion by number from "head" or by absolute reference in revision list.
    Allows retrieval of currently retained revision history for a key.
    Deletion deletes all revisions, not merely the most recent.
    If instantiated with the "revisions" keyword and an integer argument, only retains that many revisions per entry.'''

    def __init__(self, *args, **kwargs):
        revisions = kwargs.pop('revisions', None)
        self._allowed_revisions = abs(int(revisions))
        dict.__init__(self, *args, **kwargs)

    def __getitem__(self, key):
        return dict.__getitem__(self, key)[-1]

    def __setitem__(self, key, value):
        if dict.get(self, key, [])[-1:] != [value]:
            dict.setdefault(self, key, []).append(value)
        if self._allowed_revisions and len(dict.__getitem__(self, key)) > self._allowed_revisions:
            dict.__setitem__(self, key, dict.__getitem__(self, key)[-self._allowed_revisions:])

    def revert_back_by(self, key, revert_by):
        self[key] = dict.__getitem__(self, key)[-(revert_by+1)]

    def revert_to(self, key, revert_to):
        self[key] = dict.__getitem__(self, key)[revert_to]

    def trim_revisions(self, number):
        for key in self:
            dict.__setitem__(self, key, dict.__getitem__(self, key)[-number:])
            
    def get_revisions(self, key):
        return dict.__getitem__(self, key)

    def del_revision(self, key, number):
        del(dict.__getitem__(self, key)[number])