>Worth noting in a non-docstring comment that `_wave_list` acts like a private construction variable that allows Galsim functions to override the default way that `wave_list` is normally constructed.

added inside `__init__` method:
```
        # Note that `_wave_list` acts a private construction variable that overrides the way that
        # `wave_list` is normally constructed (see `Bandpass.__mul__` below)
```