How to reverse a linked-list using constant memory

reverse.py

	def reverse(self):
		
		if self.first == None or self.first.next == None:
			# list is empty or has just one element,
			# there's nothing to do
			return
		
		previous = None
		current = self.first
		next = current.next

		while next:
			# switching the pointers
			current.next = previous

			previous = current
			current = next
			next = next.next

		
		current.next = previous

		# change head of the list
		self.first = current