refactor(fibonacci): use function attribute for persistent memoization cache

Author: RomanSanaye

Sprint-2/improve_with_caches/fibonacci/fibonacci.py

@@ -1,11 +1,12 @@
 def fibonacci(n):
-    # Initialize the cache dictionary
-    cache = {}
+    # Initialize the cache as a function attribute if it doesn't exist yet
+    if not hasattr(fibonacci, "cache"):
+        fibonacci.cache = {}
 
     def helper(number):
-        # Check the cache at the start
-        if number in cache:
-            return cache[number]
+        # Check the function attribute cache at the start
+        if number in fibonacci.cache:
+            return fibonacci.cache[number]
 
         # Base case
         if number <= 1:
@@ -14,8 +15,8 @@ def helper(number):
         # Compute the result (making sure number decreases!)
         result = helper(number - 1) + helper(number - 2)
 
-        # Store the result in the cache right before returning
-        cache[number] = result
+        # Store the result in the function attribute cache right before returning
+        fibonacci.cache[number] = result
         return result
 
-    return helper(n)
+    return helper(n)