Simplify rsr plotting code regarding finding all bands and response functions to plot

[adybbroe]

Code Sample, a minimal, complete, and verifiable piece of code

NA

Problem description

The composite_rsr_plot.py script is a bit complex concerning the identification of all bands and responses to plot, now recently with the addition of the --exclude_bandnames command line argument, see PR #240

"Possible simplification: Could you have a function that gets all the bands needed to be plotted and would take the wavelength and band information in as input and produce a list of bands?"

Also, would be good to have this tested!

[djhoese]

I mentioned this on slack but will post here too for future reference. The easiest part to see what could be simplified is the set of if/elif statements that do the top level of plotting:

        if req_wvl:
            bands = rsr.get_bandname_from_wavelength(req_wvl, 0.25, multiple_bands=True)
            if not bands:
                continue
            if isinstance(bands, list):
                for b__ in bands:
                    plt = plot_band(plt, b__, rsr,
                                    platform_name_in_legend=(not no_platform_name_in_legend))
            else:
                plt = plot_band(plt, bands, rsr,
                                platform_name_in_legend=(not no_platform_name_in_legend))
        elif band:
            plt = plot_band(plt, band, rsr,
                            platform_name_in_legend=(not no_platform_name_in_legend))

If you instead put the bands logic in a function:

bands 
if req_wvl:
    bands = rsr.get_bandname_from_wavelength(req_wvl, 0.25, multiple_bands=True)
elif band:
    bands = [band]
else:
    bands = []
    wvlx = wvlmin
    while wvlx < wvlmax:
        bands.extend(rsr.get_band_name_for_wavelength(...)
        wvlx += wavel_res / 5.0
    bands = sorted(set(bands))

if not isinstance(bands, list):
    bands = [bands]
return bands

then you can do:

bands = _bands_to_plot(req_wvl, band, wvlmin, wvlmax...)
for band in bands:
    plot_band(plt, band, rsr, ...)

It gets even simpler if rsr.get_bandname_from_wavelength always returns a list. I assume all the prev_bands stuff is to make sure that a band isn't plotted twice. This is handled above by a set. Oh and excluded_bandnames would be done in the plotting for loop.