dictdb - dict with transactions

dictdb.py

class Dictdb:
    def __init__(self):
        self.db = {}
        self.rdb = {}
        self.rdiff = []

    def rinc(self, val):
        if val not in self.rdb:
            self.rdb[val] = 0
        self.rdb[val] += 1

    def rdec(self, val):
        self.rdb[val] -= 1

    def get(self, key):
        return self.db.get(key)

    def _set(self, key, val):
        if key in self.db:
            self.rdec(self.db[key])
            del self.db[key]

        if val is not None:
            self.db[key] = val
            self.rinc(val)

    def set(self, key, val):
        if self.rdiff:
            rdiff = self.rdiff[-1]
            if key not in rdiff:
                rdiff[key] = self.db.get(key)

        self._set(key, val)

    def unset(self, key):
        self.set(key, None)

    def count(self, val):
        return self.rdb[val] if val in self.rdb else 0

    def begin(self):
        self.rdiff.append({})

    def rollback(self):
        if not self.rdiff:
            return False

        rdiff = self.rdiff.pop()
        for key, val in rdiff.iteritems():
            self._set(key, val)

        return True

    def commit(self):
        self.rdiff = []