London | 25-SDC-July | Fatma Arslantas | Sprint 2 | Implement an LRU cache in Python

Sprint-2/implement_lru_cache/lru_cache.py

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+from collections import OrderedDict
+
+class LruCache:
+    # It keeps the most recently used items.
+    # If it gets full, it throws away the item we haven't used for the longest time.
+    def __init__(self, limit):
+        if limit <= 0:
+            raise ValueError("Limit must be positive")
+
+        self.limit = limit
+        # OrderedDict is like a dictionary. It remembers the order of items.
+        # It handles the O(1) logic for us automatically.
+        self.cache = OrderedDict()
+
+    def get(self, key):
+        # Trying to find an item
+        if key not in self.cache:
+            return None
+
+        # If I found it, it means I just "USED" it.
+        # So I move it to the end (Newest position).
+        self.cache.move_to_end(key)
+        return self.cache[key]
+
+    def set(self, key, value):
+        # We are adding or updating an item.
+
+        if key in self.cache:
+            # If it exists, update it and move to the end (Newest).
+            self.cache.move_to_end(key)
+
+        self.cache[key] = value
+
+        if len(self.cache) > self.limit:
+            # Remove the oldest item.
+            # last=False means "Remove from the beginning (Oldest)".
+            self.cache.popitem(last=False)