update following SRP implementation

Author: Abubakar-Meigag

Sprint-2/implement_lru_cache/lru_cache.py

@@ -1,61 +1,73 @@
 from typing import Optional
 
 class _Node:
+    
     def __init__(self, key=None, value=None):
-        self.key   = key
+        self.key = key
         self.value = value
         self.prev: Optional["_Node"] = None
         self.next: Optional["_Node"] = None
-
-class LruCache:
-    def __init__(self, limit):
-        if limit <= 0:
-            raise ValueError("limit must be positive")
-
-        self.limit = limit
-        self.cache = {}
-
+        
+class DoublyLinkedList:
+    
+    def __init__(self):
         self.head = _Node()
         self.tail = _Node()
         self.head.next = self.tail
         self.tail.prev = self.head
 
-    def remove(self, node):
+    def remove(self, node: _Node):
+        assert node.prev is not None
+        assert node.next is not None
         node.prev.next = node.next
         node.next.prev = node.prev
 
-    def add_to_front(self, node):
+    def add_to_front(self, node: _Node):
         next_node = self.head.next
         assert next_node is not None
-
         node.next = next_node
         node.prev = self.head
         next_node.prev = node
         self.head.next = node
 
+    def remove_last(self) -> _Node:
+        lru = self.tail.prev
+        assert lru is not None
+        self.remove(lru)
+        return lru
+
+
+class LruCache:
+    
+    def __init__(self, limit):
+        if limit <= 0:
+            raise ValueError("limit must be positive")
+        
+        self.limit = limit
+        self.cache = {}
+        self.list = DoublyLinkedList()
+
     def get(self, key):
         if key not in self.cache:
             return None
-
+        
         node = self.cache[key]
-        self.remove(node)
-        self.add_to_front(node)
+        self.list.remove(node)
+        self.list.add_to_front(node)
         return node.value
 
     def set(self, key, value):
         if key in self.cache:
             node = self.cache[key]
             node.value = value
-            self.remove(node)
-            self.add_to_front(node)
+            self.list.remove(node)
+            self.list.add_to_front(node)
             return
 
         node = _Node(key, value)
         self.cache[key] = node
-        self.add_to_front(node)
+        self.list.add_to_front(node)
 
         if len(self.cache) > self.limit:
-            lru = self.tail.prev
-            assert lru is not None
-            self.remove(lru)
+            lru = self.list.remove_last()
             del self.cache[lru.key]