'Fetch a bunch of keys from the cache. For certain backends (memcached,
pgsql) this can be *much* faster when fetching multiple values.
Return a dict mapping each key in keys to its value. If the given
key is missing, it will be missing from the response dict.'

def get_many(self, keys, version=None):

    d = {}
    for k in keys:
        val = self.get(k, version=version)
        if (val is not None):
            d[k] = val
    return d
