Series.str.findall(pat, flags=0, **kwargs)返回要查询的内容
参数:
pat : 字符串或正则
flags : 整型,
返回:
序列Series/索引Index of lists

import pandas as pd
s = pd.Series(['A', 'B', 'C', 'Aaba', 'Baca', 'CABA', 'dog', 'cat'])
print(s.str.findall("A"))
0       [A]
1        []
2        []
3       [A]
4        []
5    [A, A]
6        []
7        []
dtype: object