Add test for `_get_scaling`

[ricardoV94]

This function has a somewhat long and complicated sequence of conditional branches. AFAICT there is no direct test, so we should add one that covers all the expected cases to facilitate future maintenance and refactoring.

Bonus points for adding type hints

pymc/pymc/distributions/logprob.py

Lines 46 to 107 in 114e439

	def _get_scaling(total_size, shape, ndim):
	"""
	Gets scaling constant for logp
	Parameters
	----------
	total_size: int or list[int]
	shape: shape
	shape to scale
	ndim: int
	ndim hint
	Returns
	-------
	scalar
	"""
	if total_size is None:
	coef = floatX(1)
	elif isinstance(total_size, int):
	if ndim >= 1:
	denom = shape[0]
	else:
	denom = 1
	coef = floatX(total_size) / floatX(denom)
	elif isinstance(total_size, (list, tuple)):
	if not all(isinstance(i, int) for i in total_size if (i is not Ellipsis and i is not None)):
	raise TypeError(
	"Unrecognized `total_size` type, expected "
	"int or list of ints, got %r" % total_size
	)
	if Ellipsis in total_size:
	sep = total_size.index(Ellipsis)
	begin = total_size[:sep]
	end = total_size[sep + 1 :]
	if Ellipsis in end:
	raise ValueError(
	"Double Ellipsis in `total_size` is restricted, got %r" % total_size
	)
	else:
	begin = total_size
	end = []
	if (len(begin) + len(end)) > ndim:
	raise ValueError(
	"Length of `total_size` is too big, "
	"number of scalings is bigger that ndim, got %r" % total_size
	)
	elif (len(begin) + len(end)) == 0:
	return floatX(1)
	if len(end) > 0:
	shp_end = shape[-len(end) :]
	else:
	shp_end = np.asarray([])
	shp_begin = shape[: len(begin)]
	begin_coef = [floatX(t) / shp_begin[i] for i, t in enumerate(begin) if t is not None]
	end_coef = [floatX(t) / shp_end[i] for i, t in enumerate(end) if t is not None]
	coefs = begin_coef + end_coef
	coef = at.prod(coefs)
	else:
	raise TypeError(
	"Unrecognized `total_size` type, expected int or list of ints, got %r" % total_size
	)
	return at.as_tensor(floatX(coef))

Related to #4582

[Diwakar-Gupta]

@ricardoV94 can you share some resources to know what exactly _get_scaling does.

[chritter]

@Icyshaman and I are working on this issue.