DeprecationWarning: Sentinel is not a public part of the traitlets API. It was published by mistake, and may be removed in the future.

[pllim]

https://github.com/jupyter-widgets/traittypes/blob/af2ebeec9e58b73a12d4cf841bd506d6eadb8868/traittypes/traittypes.py#L21

traittypes/__init__.py:1: in <module>
    from .traittypes import *
traittypes/traittypes.py:20: in <module>
    Empty = Sentinel('Empty', 'traittypes',
traitlets/__init__.py:24: in __init__
    warn(
traitlets/utils/warnings.py:11: in warn
    return warnings.warn(msg, category=category, stacklevel=stacklevel, source=source)
E   DeprecationWarning:
E               Sentinel is not a public part of the traitlets API.
E               It was published by mistake, and may be removed in the future.