implementing param depends

[kcpevey]

Seems like panels interact() is handy, but from what I've seen in the panel docs https://panel.pyviz.org/user_guide/Interact.html I don't understand how it relates to the previous discussions on @depends. Namely how you get the dependency between existing param objects (I don't want to interact to generate them on the fly).

I guess I'm just still struggling understand and implementing param dependencies. Are there any more notebook examples I can take a look at?

[philippjfr]

Namely how you get the dependency between existing param objects (I don't want to interact to generate them on the fly).

The interact functionality is an alternative to the class/param based approach for people not familiar with parameterized objects and classes. So the two approaches are completely orthogonal.

I guess I'm just still struggling understand and implementing param dependencies.

I've started to write some documentation and examples but am struggling coming up with examples that are simple, interesting and get the point across. In any case I'll add something to the Param user guide later today or tomorrow.

[kcpevey]

simple example:

class projections(param.Parameterized):
    projection      = param.ObjectSelector(default="UTM", objects=["Geographic", "Mercator", "UTM"], precedence=1)
    UTM_zone_hemi   = param.ObjectSelector(default='North', objects=['North', 'South'], precedence=2)
    UTM_zone_num    = param.Integer(52, bounds=(1, 60), precedence=3)

    def get_crs(self):
        if self.projection == 'UTM':
            if self.UTM_zone_hemi == 'South':
                hemi = True
            else:
                hemi = False
            proj = ccrs.UTM(self.UTM_zone_num, southern_hemisphere=hemi)

        elif self.projection == 'Geographic':
            proj = ccrs.PlateCarree()

        elif self.projection == 'Mercator':
            proj = ccrs.GOOGLE_MERCATOR

        return proj

If projection=='UTM', then I want UTM_zone_hemi and UTM_zone_num to appear, otherwise, they should remain hidden.

Tagging @JoshuaQChurch since I asked him about this too

[philippjfr]

If projection=='UTM', then I want UTM_zone_hemi and UTM_zone_num to appear, otherwise, they should remain hidden.

To clarify, you want this to appear where? Or to ask a different way, what will be consuming the output of get_crs?

[kcpevey]

I want UTM_zone_hemi and UTM_zone_num widgets to be hidden until projection='UTM'. Those widgets can appear right under projection.

get_crs is a method I use later to convert the widget input to a ccrs projection (which becomes input to the crs parameter in annotators or gv maps).

Does that answer your question?

[philippjfr]

Yes, thanks. So hiding it dynamically is currently not supported (but probably could be by dynamically setting the precedence). For now you could simply make them constant like this:

class projections(param.Parameterized):
    projection      = param.ObjectSelector(default="UTM", objects=["Geographic", "Mercator", "UTM"], precedence=1)
    UTM_zone_hemi   = param.ObjectSelector(default='North', objects=['North', 'South'], precedence=2)
    UTM_zone_num    = param.Integer(52, bounds=(1, 60), precedence=3)

    @param.depends('projection', watch=True)
    def _watch_utm_projection(self):
        is_utm = self.projection == 'UTM'
        self.params('UTM_zone_hemi').constant = not is_utm
        self.params('UTM_zone_num').constant = not is_utm

    def get_crs(self):
        if self.projection == 'UTM':
            if self.UTM_zone_hemi == 'South':
                hemi = True
            else:
                hemi = False
            proj = ccrs.UTM(self.UTM_zone_num, southern_hemisphere=hemi)

        elif self.projection == 'Geographic':
            proj = ccrs.PlateCarree()

        elif self.projection == 'Mercator':
            proj = ccrs.GOOGLE_MERCATOR

        return proj

[kcpevey]

What is this supposed to do? UTM_zone_hemi and UTM_zone_num behave the same regardless of the selection on projection.

Also - I know I've seen a demo of menus appearing and disappearing based on a selection in a demo. What am I thinking of? Do I just need to reorganize these into two classes?

[philippjfr]

What is this supposed to do?

When rendered using panel, the widgets should be disabled when self.projection != 'UTM' and look something like this:

[kcpevey]

That is not happening for me. I last updated all my packages to master on Friday I think. I might be out of date. I'll update and recheck.

[philippjfr]

Also - I know I've seen a demo of menus appearing and disappearing based on a selection in a demo. What am I thinking of? Do I just need to reorganize these into two classes?

That's right, that works by having one parameterized instance being a parameter value on another parameterized.

[kcpevey]

Still not working for me.

panel 0.1.2.post3+g8ecccf4.dirty param 1.8.1

This isn't relying on any other packages, is it?

[philippjfr]

You need to make an instance of the class for this to work.

[kcpevey]

works for me.