'Implementation for sequence generation based on sequence and options.
The implementation can assume that _initialize has been called before this
method is called.
Args:
input_sequence: An input NoteSequence to base the generation on.
generator_options: A GeneratorOptions proto with options to use for
generation.
Returns:
The generated NoteSequence proto.'

@abc.abstractmethod
def _generate(self, input_sequence, generator_options):

    pass
