Why is hashing failing in LRU Cacheing Problem in Python - python-3.x

Question

I recently stumbled across an example online for solving the LRUCache problem for interview questions. When I copied the end code into an IDE and compile/run the code, it was giving a KeyError while running through the test code in the main section.
class DLL:
def __init__(self, key, value):
self.key = key
self.value = value
self.next = None
self.prev = None
class LRUCache:
def __init__(self, capacity: int):
self.head = DLL(-1, -1)
self.tail = self.head
self.tracker = {}
self.capacity = capacity
self.length = 0
def get(self, key: int) -> int:
if key not in self.tracker:
return -1
node = self.tracker[key]
value = node.value
while node.next:
node.prev.next = node.next
node.next.prev = node.prev
self.tail.next = node
node.prev = self.tail
node.next = None
self.tail = node
return value
def put(self, key: int, value: int) -> None:
if key not in self.tracker:
node = self.tracker[key]
node.value = value
while node.next:
node.prev.next = node.next
node.next.prev = node.prev
self.tail.next = node
node.prev = self.tail
node.next = None
self.tail = node
else:
node = DLL(key, value)
self.tracker[hash] = node
self.tail.next = node
node.prev = self.tail
self.tail = node
self.length += 1
if self.length > self.capacity:
remove = self.head.next
self.head.next = self.head.next.next
self.head.next.prev = self.head
del self.tracker[remove.key]
self.length += 1
if __name__ == '__main__':
lru = LRUCache(3)
lru.put(1, 2)
lru.put(2, 2)
lru.put(3, 2)
lru.get(3)
lru.get(1)
lru.put(4, 2)
lru.get(4)
With an error message spitting out:
Traceback (most recent call last):
File "LRUCache.py", line 63, in <module>
lru.put(1, 2)
File "LRUCache.py", line 36, in put
node = self.tracker[key]
KeyError: 1
The problem is linked to the line self.tracker[hash] = node but I cannot figure out why. Can someone please explain what is going on here? The original posting does not have a comments section, so I have been stuck trying to figure out someone else's code on my own.