I've recently released a library that does .NET viewstate decoding, feel free to try it out https://github.com/yuvadm/viewstate/
Sample usage:
>>> from viewstate import ViewState
>>> base64_encoded_viewstate = '/wEPBQVhYmNkZQ9nAgE='
>>> vs = ViewState(base64_encoded_viewstate)
>>> vs.decode()
('abcde', (True, 1))