class Stack:
def __init__(self):
self.size = 0
#self.data = []
self.data = LinkedList()
def __len__(self):
#return len(self.data)
return self.size
def push(self, value):
#self.data.append(value)
self.data.insert_head(value)
self.size += 1
def pop(self):
#if len(self.data) is 0:
# return None
#else:
# val = self.data[len(self.data) - 1]
# self.data.pop(len(self.data) - 1)
# return val
if self.data.head is None:
return None
else:
val = self.data.head.get_data()
self.data.remove_head()
self.size -= 1
return val
