Interface to versioned dictionary

from UserDict import DictMixin
class VDict(DictMixin):
    def __getitem__(self, key):
        if isinstance(key, tuple):
            docid, rev = key
        else:
            docid = key
            rev = None  # set to tip rev

        print docid, rev
        # return ...

In [1]: d = VDict()

In [2]: d[2]
2 None

In [3]: d[2, 1]
2 1

def getrev(self, docid, rev):
   ...

class RevisionView(object):
    def __init__(self, db, revid):
        self.db = db
        self.revid = revid
    def __getitem__(self, item):
        self.db.getrev(item, self.revid)