如何获取DataFrame GroupBy对象的列名？

import pandas as pd

# 创建一个DataFrame
data = {'A': ['foo', 'bar', 'foo', 'bar', 'foo', 'bar', 'foo', 'foo'],
        'B': ['one', 'one', 'two', 'two', 'two', 'one', 'two', 'one'],
        'C': [1, 2, 3, 4, 5, 6, 7, 8],
        'D': [10, 20, 30, 40, 50, 60, 70, 80]}
df = pd.DataFrame(data)

# 按列'A'进行分组
grouped = df.groupby('A')

# 获取分组的列名
column_names = list(grouped.groups.keys())
print(column_names)

['bar', 'foo']