将列的值复制到pandas中的下几行

import pandas as pd

# 创建一个示例数据框
data = {'A': [1, 2, None, None, None],
        'B': [4, 5, None, None, None],
        'C': [7, 8, None, None, None]}

df = pd.DataFrame(data)

# 使用fillna函数将列的值复制到下几行
df['A'].fillna(method='ffill', inplace=True)
df['B'].fillna(method='ffill', inplace=True)
df['C'].fillna(method='ffill', inplace=True)

print(df)

     A    B  C
0  1.0  4.0  7
1  2.0  5.0  8
2  2.0  5.0  8
3  2.0  5.0  8
4  2.0  5.0  8