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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def create_default_bls_bft_factory(node):
    '''
    Creates a default BLS factory to instantiate BLS BFT classes.

    :param node: Node instance
    :return: BLS factory instance
    '''
    bls_keys_dir = os.path.join(node.keys_dir, node.name)
    bls_crypto_factory = create_default_bls_crypto_factory(bls_keys_dir)
    return BlsFactoryBftPlenum(bls_crypto_factory, node)