Inconsistent signature of `apply`

[maaleske]

Dataset.apply allows passing positional arguments to func as args=(), whereas DataArrayGroupBy.apply and DatasetGroupBy.apply do not. The documentation also incorrectly suggests that the reverse is true:

Dataset.apply:

xarray/xarray/core/dataset.py

Lines 2832 to 2840 in 4de8dbc

	def apply(self, func, keep_attrs=False, args=(), **kwargs):
	"""Apply a function over the data variables in this dataset.
	Parameters
	----------
	func : function
	Function which can be called in the form `f(x, **kwargs)` to
	transform each DataArray `x` in this dataset into another
	DataArray.

DataArrayGroupBy.apply:

xarray/xarray/core/groupby.py

Lines 473 to 478 in 4de8dbc

	def apply(self, func, shortcut=False, **kwargs):
	"""Apply a function over each array in the group and concatenate them
	together into a new array.
	`func` is called like `func(ar, *args, **kwargs)` for each array `ar`
	in this group.

DatasetGroupBy.apply:

xarray/xarray/core/groupby.py

Lines 580 to 585 in 4de8dbc

	def apply(self, func, **kwargs):
	"""Apply a function over each Dataset in the group and concatenate them
	together into a new Dataset.
	`func` is called like `func(ds, *args, **kwargs)` for each dataset `ds`
	in this group.

I feel that funcs passed to GroupBy objects are generally equally deserving of positional arguments, and I don't see a reason why this isn't the case.