python dataframe递归找出每个节点的所有父节点

数据存储格式

pid	id
None	a
a	a1
a	a2
a1	a11
a11	a111
a	a12

期望获得每个id的所有pid

代码如下:

import pandas as pd

df = pd.DataFrame(
    {
        'id': ['a', 'a1', 'a2', 'a11', 'a111', 'a12'],
        'pid': [None, 'a', 'a', 'a1', 'a11', 'a']
    }
)


# 获取id的所有父节点
def get_pid_list(df, id):
    tmp_df = df[df['id'] == id]

    if tmp_df.empty or tmp_df['pid'].values[0] is None:
        return pd.DataFrame(columns=['id', 'pid'])
    else:
        return get_pid_list(df, tmp_df['pid'].values[0]).append(tmp_df)


id_list = df['id'].values
for i in id_list:

    pid_list = get_pid_list(df, i)['pid'].values.tolist()
    print(i, pid_list)

输出结果:
a []
a1 ['a']
a2 ['a']
a11 ['a', 'a1']
a111 ['a', 'a1', 'a11']
a12 ['a']