def enqueue(self, item):
oldlast = self.last
self.last = Node(item, None)
if self.is_empty():
self.first = self.last
else:
oldlast.next = self.last
self.n += 1
def push(self, item):
oldfirst = self.first
self.first = Node(item, oldfirst)
self.n += 1