在多索引数据帧中添加缺少的日期索引

import pandas as pd
import numpy as np

# 原始数据帧
df = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]}, index=pd.Index(['2022-01-01', '2022-01-03', '2022-01-05'], name='date'))

# 创建日期索引
start_date = '2022-01-01'
end_date = '2022-01-05'
date_index = pd.date_range(start=start_date, end=end_date, freq='D')

# 创建多级索引
multi_index = pd.MultiIndex.from_product([df.index, date_index], names=['date', 'new_date'])

# 重新索引数据帧
new_df = df.reindex(multi_index, method='ffill')

print(new_df)