In such classes like ProposalBuilder, TransactionBuilder we can see usage of BlockchainInstance in such way
BlockchainInstance.__init__(self, **kwargs)
But it's not pythonic way, there are a lot of warnings - from Expected type 'BlockchainInstance', got 'TransactionBuilder' instead to Unresolved attribute reference 'blockchain' for class 'TransactionBuilder'.
I suggest inherit from class BlockchainInstance instead of using it in this way.