This one took some thought.  To me, the `create*` names seem more explicit about creating new `Bandpass`es than just `truncate` or `thin`, which sound like they're modifying the `Bandpass` in place.  I also considered `truncated` and `thinned`, which sound to me more like they're returning new objects.  On the other hand, I see that the python (immutable) `str` methods take names like `capitalize()`, i.e. present-tense verbs, to return new objects.  So I guess the present-tense verb paradigm probably is the most "pythonic".