def connect(self): 
        try:
            self.connection = pymongo.Connection(self.host, self.port)
            self.db = self.connection[self.name]
        except AutoReconnect:
            raise DatabaseException("It's not possible connect to the database")
def test_impl(n):
            df = pd.DataFrame({'A': np.arange(n)})
            df.A[2] = 0
            return df.A.nunique()