python如何计算夏普比率？

import numpy as np

import pandas as pd

np.random.seed(0)

# Simulate cumulative returns of 100 days

N = 100

D = pd.DataFrame(np.random.normal(size=N))

R = D.cumsum()

# Calcute returns ratio

r = (R - R.shift(1))/R.shift(1)

sr = r.mean()/r.std() * np.sqrt(252)

print("sharpe ratio =", sr)