Just keep in mind that idiomatic Python expects https://en.wikipedia.org/wiki/Command%E2%80%93query_separati... if you return instances to support chaining, please return new instances rather than modifying the original in-place. Take the example set by the builtins; `list.append` etc. return `None` for a reason. cf. https://stackoverflow.com/questions/11205254.
Good point.
Since the idea behind method chaining is a bit like UNIX pipes anyways, it would be silly (and unexpected) if commands later in the chain affected parts that came before, so you basically output a new instance each time. In my example above the signal wouldn't be a sine wave anymore after the first step, so that would make even less sense.
Editing existing instances is something I'd do for performance reasons only with no return value (lets exclude errors).