如何获取一行中的最后一个可用值来填充NaN值

import pandas as pd
import numpy as np

# 创建一个示例数据
data = {'A': [1, np.nan, np.nan, 4, np.nan],
        'B': [np.nan, 2, np.nan, np.nan, 5],
        'C': [3, np.nan, 6, np.nan, np.nan]}
df = pd.DataFrame(data)

# 遍历每一行
for index, row in df.iterrows():
    last_valid_value = np.nan
    # 从最后一个元素开始向前遍历
    for i in range(len(row)-1, -1, -1):
        if not pd.isna(row[i]):
            last_valid_value = row[i]
        else:
            row[i] = last_valid_value

print(df)

     A    B    C
0  1.0  2.0  3.0
1  4.0  2.0  6.0
2  4.0  2.0  6.0
3  4.0  2.0  6.0
4  4.0  5.0  6.0