从一个DataFrame列填充另一个列，但每隔n行值填充一次

import pandas as pd

df = pd.DataFrame({'A': [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 'B': [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]})

    A   B
0   1  11
1   2  12
2   3  13
3   4  14
4   5  15
5   6  16
6   7  17
7   8  18
8   9  19
9  10  20

n = 2  # 每隔n行填充一次
for i in range(len(df)):
    if i % n == 0:
        df.loc[i, 'B'] = df.loc[i, 'A']

    A   B
0   1   1
1   2  12
2   3   3
3   4  14
4   5   5
5   6  16
6   7   7
7   8  18
8   9   9
9  10  20