Initialize `SpaceGroupType` from spacegroup symbols

[janosh]

currently the recently added (2559486) can only be created from spacegroup numbers:

moyo/moyopy/python/moyopy/_data.pyi

Lines 46 to 60 in e99cc67

	class SpaceGroupType:
	"""Space-group type information."""
	def __init__(self, number: int): ...
	# Space group type
	@property
	def number(self) -> int:
	"""ITA number for space group types (1 - 230)."""
	@property
	def hm_short(self) -> str:
	"""Hermann-Mauguin symbol in short notation."""
	@property
	def hm_full(self) -> str:
	"""Hermann-Mauguin symbol in full notation."""
	# Arithmetic crystal class
	@property

would be very useful to be able to pass strings in as well. happy to submit a PR if this sounds sensible

from moyopy import SpaceGroupType

# these throw TypeError: argument 'number': 'str' object cannot be interpreted as an integer
sgt1 = SpaceGroupType("Fm-3m")
sgt2 = SpaceGroupType("P6_3/m")
sgt3 = SpaceGroupType("Fmmm")

[lan496]

I think the current space-group number input is enough: We can match a given Hermann-Mauguin (HM) symbol by looping over SpaceGroupType.
I am concerned that a lot of str inputs will be infeasible or require an additional search. That is, these HM-symbol-like string may not form a space group or not give a space group in the ITA setting.

[janosh]

could this not be solved by a lookup table map_hm_short_to_int: dict[str, int] that essentially copies this Wiki table? the reason i think this would be good to have is that the SpaceGroup class in pymatgen is initialized from a HM symbol string and so users coming from pymatgen will likely expect the same to work in moyopy. the good thing is there is already a suite of unit tests in test_groups.py that could be copied over to check for correctness

[lan496]

How about using SpaceGroupType.hm_short?

map_hm_short_to_number = [moyopy.SpaceGroupType(number).hm_short for number in range(1, 230+1)]

It is not heavy computation, so it would be enough to provide this recipe in example docs.

[janosh]

sounds good. on that note, what do you think of adding hm_short attribute to MoyoDataset. it would avoid the need to import SpaceGroupType in use cases like this

[lan496]

I prefer to separate hm_short from MoyoDataset because it can be derived from MoyoDataset.number. I agree direct access to hm_short would be handy, but in that case I am not sure how to choose other entries in SpaceGroupType as MoyoDataset members.

[janosh]

assuming there's no performance penalty, why not add all of them? basically i'm suggesting MoyoDataset become the main user-facing API. if the needs of most Python users are served by just importing MoyoDataset and MoyoAdapter, i think that would make moyopy powerful yet easy to learn

[lan496]

I think the smaller number of imports does not necessarily mean easier usability. I want to keep the Python interface as simple as possible, and I feel such a fully loaded class would be in a third-party library (for example, pymatgen's SpacegroupAnalyzer with moyopy backend).