caching for when functools.cache() is not available (looking at you, pypy!)

tools/int_seq.py

@@ -1,5 +1,5 @@
 import math
-from typing import Dict
+from .tools import cache
 
 
 def factorial(n: int) -> int:
@@ -10,7 +10,8 @@ def factorial(n: int) -> int:
     return math.factorial(n)
 
 
-def fibonacci(n: int, cache: Dict[int, int] = None) -> int:
+@cache
+def fibonacci(n: int) -> int:
     """
     F(n) = F(n-1) + F(n-2) with F(0) = 0 and F(1) = 1
     0, 1, 1, 2, 3, 5, 8, 13, 21, ...
@@ -18,13 +19,7 @@ def fibonacci(n: int, cache: Dict[int, int] = None) -> int:
     if n < 2:
         return n
 
-    if cache is None:
-        cache = {}
-
-    if n not in cache:
-        cache[n] = fibonacci(n - 1, cache) + fibonacci(n - 2, cache)
-
-    return cache[n]
+    return fibonacci(n - 1) + fibonacci(n - 2)
 
 
 def triangular(n: int) -> int:

tools/tools.py

@@ -2,6 +2,7 @@ import datetime
 import inspect
 import os.path
 import sys
+from functools import wraps
 from typing import Any
 
 
@@ -42,3 +43,18 @@ def human_readable_time_from_delta(delta: datetime.timedelta) -> str:
         time_str += "00:"
 
     return time_str + "%02d" % (delta.seconds % 60)
+
+
+def cache(func):
+    saved = {}
+
+    @wraps(func)
+    def newfunc(*args):
+        if args in saved:
+            return saved[args]
+
+        result = func(*args)
+        saved[args] = result
+        return result
+
+    return newfunc