From fa68aa61094a4cbf4d16dd7194ce482e06679275 Mon Sep 17 00:00:00 2001
From: Stefan Harmuth <stefan.harmuth@net-m.de>
Date: Tue, 21 Dec 2021 10:08:18 +0100
Subject: [PATCH] caching for when functools.cache() is not available (looking
 at you, pypy!)

---
 tools/int_seq.py | 13 ++++---------
 tools/tools.py   | 16 ++++++++++++++++
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/tools/int_seq.py b/tools/int_seq.py
index 83c7425..ee701a7 100644
--- a/tools/int_seq.py
+++ b/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:
diff --git a/tools/tools.py b/tools/tools.py
index 69e9b0e..0266884 100644
--- a/tools/tools.py
+++ b/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