D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D

def setdefault(self, k, d=None):
        """ D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D """
        if k not in self._col_dict:
            self._set_key(k, d)
        return self._col_dict.get(k)