Check "cell" input signature in python interface

[atztogo]

As raised in #411, this should be fixed by something like not isinstance(cell, tuple) and not len(cell) in (3, 4) as @sphuber suggested.

cell is defined at https://spglib.readthedocs.io/en/latest/python-interface.html#crystal-structure-cell. I think cell can be given by list or something like that. How should we do? Do you have any idea @lan496, @LecrisUT?

[lan496]

I also agree to raise an exception when cell has an invalid type. This can be harmlessly done by emitting an exception from spglib._check:

spglib/python/spglib/spglib.py

Lines 1999 to 2013 in 63a7a4b

	def _check(lattice, positions, numbers, magmoms):
	if lattice.shape != (3, 3):
	return False
	if positions.ndim != 2:
	return False
	if positions.shape[1] != 3:
	return False
	if numbers.ndim != 1:
	return False
	if len(numbers) != positions.shape[0]:
	return False
	if magmoms is not None:
	if len(magmoms) != len(numbers):
	return False
	return True

The only thing to be discussed will be a name for the exception. For example CellError?

[LecrisUT]

Use standard TypeError and such. Probably individual for each one. I don't think the user would have much use for a CellError there since they are already in charge of the type they pass.

Custom exception would be useful for convergence or internal errors.

[lan496]

Indeed. TypeError will be appropriate.

[lan496]

I'll work on it.