[yt-dev] YT field detection

[Douglas Harvey Rudd]

Hi all

I have a set of fixes for Issue #887 (field detection). Most apply without breaking any tests, but to address all of the problems in that issue I need to add a check to YTDataContainer._determine_fields that doesn't allow a field to be added if it doesn't exist in field_list or derived_field_list.

This fixes my bug, but breaks a test based on code in yt/visualization/volume_rendering/camera.py which adds a field "temp_weightfield" (not a tuple!).

When this field is passed to _determine_fields, _get_field_info first guesses at ("gas","temp_weightfield"), but since that doesn't exist in field_info, it replaces it with ("index","temp_weightfield"), which I don't see as being any better.

There are several places where the syntax _get_field_info(*field) is used, which will break when field is a string, not a tuple.  Should I fix camera.py to use an explicit fluid type?  If so, what?  I've tried to use the fluid type of the input field, but that apparently is also not always a tuple.

e.g.
        fields = [field]
        if self.weight is not None:
            self.weightfield = (field[0], "temp_weightfield")
            # This is a temporary field, which we will remove at the end.
            def _make_wf(f, w):
                def temp_weightfield(a, b):
                    tr = b[f].astype("float64") * b[w]
                    return b.apply_units(tr, a.units)
                    return tr
                return temp_weightfield
            ds.field_info.add_field(self.weightfield,
                function=_make_wf(self.field, self.weight))
            # Now we have to tell the dataset to add it and to calculate
            # its dependencies..
            deps, _ = ds.field_info.check_derived_fields([self.weightfield])
            ds.field_dependencies.update(deps)
            fields = [self.weightfield, self.weight]

Douglas Rudd
Scientific Computing Consultant
Research Computing Center
drudd at uchicago.edu