Idea for extract_levels check

[bouweandela]

This adds an extra check on extract_levels settings

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• Create an issue to discuss what you are going to do, if you haven't done so already (and add the link at the bottom)
• Add unit tests
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---

Closes {Link to corresponding issue}

[valeriupredoi]

careful here with generic coordinates like olevel or alevel -> are they mapped to eg coord name plev at this stage? Can't remember @jvegasbsc

[schlunma]

@bouweandela do you have any intentions to further work on this for v2.5?

[schlunma]

I just had another look at this PR and it seems that it's not necessary anymore. We already have a check for the existence of a Z coordinate here (l.1022):

ESMValCore/esmvalcore/preprocessor/_regrid.py

Lines 972 to 1025 in 7d43072

	def get_reference_levels(filename, project, dataset, short_name, mip,
	frequency, fix_dir):
	"""Get level definition from a reference dataset.
	Parameters
	----------
	filename: str
	Path to the reference file
	project : str
	Name of the project
	dataset : str
	Name of the dataset
	short_name : str
	Name of the variable
	mip : str
	Name of the mip table
	frequency : str
	Time frequency
	fix_dir : str
	Output directory for fixed data
	Returns
	-------
	list[float]
	Raises
	------
	ValueError:
	If the dataset is not defined, the coordinate does not specify any
	levels or the string is badly formatted.
	"""
	filename = fix_file(
	file=filename,
	short_name=short_name,
	project=project,
	dataset=dataset,
	mip=mip,
	output_dir=fix_dir,
	)
	cubes = load(filename, callback=concatenate_callback)
	cubes = fix_metadata(
	cubes=cubes,
	short_name=short_name,
	project=project,
	dataset=dataset,
	mip=mip,
	frequency=frequency,
	)
	cube = cubes[0]
	try:
	coord = cube.coord(axis='Z')
	except iris.exceptions.CoordinateNotFoundError:
	raise ValueError('z-coord not available in {}'.format(filename))
	return coord.points.tolist()

Please re-open if necessary.

[bouweandela]

The advantage of this check was that it does not need to open the file containing the data when parsing the recipe, it checks if the level is in the CMOR table instead. So I think this would still be useful (especially considering #430).

[schlunma]

Makes sense. As I said, please re-open if necessary. Do you think this is something for v2.5?