def getCliInstance():
	global _dbcli
	if not _dbcli:
		_dbcli = DatabaseHelper()
	return _dbcli
def test_impl(n):
            df = pd.DataFrame({'A': np.arange(n) + 1.0, 'B': np.random.ranf(n)})
            Ac = df.A.pct_change(1)
            return Ac.sum()