def corofunc1():
            called[0] += 1
            return event.ReturnValue(insert_events=[evt2], append_events=[evt])
def test_impl(n):
            df = pd.DataFrame({'A': np.arange(n) + 1.0, 'B': np.random.ranf(n)})
            Ac = df.A.shift(1)
            return Ac.sum()