Return vCards and etags of all Abook entries in uids
        filename  -- unused, for API compatibility only
        uids -- the UIDs of the Abook entries (all if None)

def to_vobjects(self, filename, uids=None):
        """Return vCards and etags of all Abook entries in uids
        filename  -- unused, for API compatibility only
        uids -- the UIDs of the Abook entries (all if None)
        """
        self._update()

        if not uids:
            uids = self.get_uids(filename)

        items = []

        for uid in uids:
            entry = self._book[uid.split('@')[0]]
            # TODO add getmtime of photo
            etag = sha1(str(dict(entry)).encode('utf-8'))
            items.append((uid, self._to_vcard(entry), '"%s"' % etag.hexdigest()))
        return items