Bounds on derived coords

[HGWright]

🚀 Pull Request

Description

This PR does the loading agreed in #3678 (from this comment)

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[trexfeathers]

Suggested change

	if cf_root not in self.cf_group.bounds:
	# Check if cf_root has a bounds attribute.
	if cf_root in self.cf_group.coordinates:
	# Need to generalise this for if it's a dim or aux coord.
	bounds_name = getattr(
	self.cf_group.coordinates[cf_root], "bounds", None
	)
	if bounds_name is not None:
	form_terms = getattr(
	self.cf_group.coordinates[cf_root], "formula_terms"
	)
	form_terms = form_terms.replace(":", "")
	form_terms = form_terms.split(" ")
	example_dict = {"a": "A", "b": "B", "ps": "PS", "p0": "P0"}
	for cf_vari in formula_terms.values():
	for (
	cf_roots,
	cf_terms,
	) in cf_vari.cf_terms_by_root.items():
	if cf_terms == cf_term:
	if (
	cf_roots in self.cf_group.bounds
	and cf_roots == bounds_name
	):
	if cf_terms in form_terms:
	to_attach_to = example_dict[cf_terms]
	attach_from = cf_vari.cf_name
	if (
	to_attach_to.lower()
	!= attach_from.lower()
	):
	cf_var.bounds = cf_vari
	print(cf_vari.bounds)
	bounds_name = None
	cf_root_coord = self.cf_group.coordinates.get(cf_root, None)
	with contextlib.suppress(AttributeError):
	# Copes with cf_root_coord not existing, OR not having
	# `bounds` attribute.
	bounds_name = _getncattr(cf_root_coord, "bounds")
	if bounds_name is not None:
	# This will error if more or less than 1 variable is found.
	# TODO: does this ever need to be more permissive?
	(bounds_var,) = [
	f for f in formula_terms.values()
	if f.cf_terms_by_root.get(bounds_name) == cf_term
	]
	self.cf_group[cf_var.cf_name].bounds = bounds_var.cf_name
	# TODO: get bounds_var into the appropriate 'cf_group' for
	# discovery during helpers.get_cf_bounds_var().
	self.cf_group[bounds_var.cf_name] = CFBoundaryVariable(
	bounds_var.cf_name, bounds_var.cf_data
	)

[trexfeathers]

This might also work:

-cf_root_coord = self.cf_group.coordinates.get(cf_root, None)
+cf_root_coord = self.cf_group.coordinates.get(cf_root)

[trexfeathers]

Note that I did not exclude variables that are duplicated between the original formula terms and the bounds formula terms. E.g. ps and p0 in #3678.

This needs doing.