def to_list(val):
	"""
	Converts a string argument to a list by splitting it by spaces.
	Returns the object if not a string::

		from waflib.Utils import to_list
		lst = to_list('a b c d')

	:param val: list of string or space-separated string
	:rtype: list
	:return: Argument converted to list
	"""
	if isinstance(val, str):
		return val.split()
	else:
		return val