Discard the elements of other from self.

		if isinstance(it, _basebag):
			This runs in O(it.num_unique_elements())
		else:
			This runs in O(len(it))

def _isub(self, other):
		"""Discard the elements of other from self.

		if isinstance(it, _basebag):
			This runs in O(it.num_unique_elements())
		else:
			This runs in O(len(it))
		"""
		if isinstance(other, _basebag):
			for elem, other_count in other.counts():
				try:
					self._increment_count(elem, -other_count)
				except ValueError:
					self._set_count(elem, 0)
		else:
			for elem in other:
				try:
					self._increment_count(elem, -1)
				except ValueError:
					pass
		return self