cannot import name 'base64_chars'

[celeste95]

from secretsharing import PlaintextToHexSecretSharer as ssss
from secretsharing import SecretSharer
from secretsharing import base64_chars

I want to share Custom formats secrets, but Python3 told me
Traceback (most recent call last):
File "E:\python\exp.py", line 3, in <module>
from secretsharing import base64_chars
ImportError: cannot import name 'base64_chars'

Can u give me some suggestions?