如何扁平化pandas数据帧多列中的字典列表

import pandas as pd

data = {'col1': [{'key1': 'value1', 'key2': 'value2'}, {'key3': 'value3', 'key4': 'value4'}],
        'col2': [{'key5': 'value5', 'key6': 'value6'}, {'key7': 'value7', 'key8': 'value8'}]}
df = pd.DataFrame(data)

           col1          col2
0  {'key1': 'value1', 'key2': 'value2'}  {'key5': 'value5', 'key6': 'value6'}
1  {'key3': 'value3', 'key4': 'value4'}  {'key7': 'value7', 'key8': 'value8'}

def flatten_dict(row):
    flattened_dict = {}
    for d in row:
        flattened_dict.update(d)
    return pd.Series(flattened_dict)

df_flattened = df.apply(lambda row: flatten_dict(row), axis=1)

df_final = pd.concat([df, df_flattened], axis=1)

           col1          col2   key1   key2   key3   key4   key5   key6   key7   key8
0  {'key1': 'value1', 'key2': 'value2'}  {'key5': 'value5', 'key6': 'value6'}  value1  value2    NaN    NaN  value5  value6    NaN    NaN
1  {'key3': 'value3', 'key4': 'value4'}  {'key7': 'value7', 'key8': 'value8'}     NaN    NaN  value3  value4    NaN    NaN  value7  value8