在pandas dataframe中的列列表上应用转换时出现属性错误

import pandas as pd

# 创建一个示例数据帧
data = {'A': [1, 2, 3], 'B': [4, 5, 6], 'C': [7, 8, 9]}
df = pd.DataFrame(data)

# 检查列名是否正确
if 'D' in df.columns:
    # 对列D应用转换操作
    df['D'] = df['D'].apply(lambda x: x * 2)
else:
    print("列D不存在")

# 使用列索引应用转换操作
col_index = 1
if col_index < len(df.columns):
    df.iloc[:, col_index] = df.iloc[:, col_index].apply(lambda x: x * 2)
else:
    print("列索引超出范围")

# 对多个列应用相同的转换操作
columns_to_transform = ['A', 'B']
df[columns_to_transform] = df[columns_to_transform].apply(lambda x: x * 2)

# 对特定条件下的列应用转换操作
condition = df['A'] > 2
df.loc[condition, columns_to_transform] = df.loc[condition, columns_to_transform].apply(lambda x: x * 2)

print(df)