The base builtin is created at runtime, so PyCharm does not know about it. There may be some way to give PyCharm more information about the base reference and its type.
I am trying to get started with Panda3D and have the same issue in Pycharm.
It would be great if base could be recognized in some way to allow for autocompletion etc…
If anyone has worked through this I would love to know what you did?