如何根据dataframe中的条件填充列？

import pandas as pd

df = pd.DataFrame({'A': [1, 2, 3, 4, 5],
                   'B': [10, 20, 30, 40, 50],
                   'C': [100, 200, 300, 400, 500]})

df['D'] = ''  # 创建一个新的列D，并初始化为空字符串

# 根据条件判断填充列D
df.loc[df['A'] > 3, 'D'] = 'High'
df.loc[(df['A'] <= 3) & (df['B'] > 20), 'D'] = 'Medium'
df.loc[(df['A'] <= 3) & (df['B'] <= 20), 'D'] = 'Low'

   A   B    C       D
0  1  10  100     Low
1  2  20  200     Low
2  3  30  300  Medium
3  4  40  400    High
4  5  50  500    High