From 987d2519c20ae08d75f0bb7dafdd326294ab59a9 Mon Sep 17 00:00:00 2001
From: Jon Huber <jon@jonhuber.com>
Date: Mon, 27 Jun 2022 12:32:11 -0500
Subject: [PATCH] Introduce args slicing for trimming cache key

---
 functools32/functools32.py | 24 +++++++++++++++++---
 test_functools32.py        | 46 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/functools32/functools32.py b/functools32/functools32.py
index c44551f..8c611ec 100644
--- a/functools32/functools32.py
+++ b/functools32/functools32.py
@@ -334,7 +334,7 @@ def __ne__(self, other):
 
 _CacheInfo = namedtuple("CacheInfo", "hits misses maxsize currsize")
 
-def lru_cache(maxsize=100):
+def lru_cache(maxsize=100, key_arg_slice_start=None, key_arg_slice_stop=None):
     """Least-recently-used cache decorator.
 
     If *maxsize* is set to None, the LRU features are disabled and the cache
@@ -366,7 +366,16 @@ def decorating_function(user_function,
 
             @wraps(user_function)
             def wrapper(*args, **kwds):
-                key = args
+
+                if key_arg_slice_start and key_arg_slice_stop:
+                    key = args[key_arg_slice_start:key_arg_slice_stop]
+                elif key_arg_slice_start:
+                    key = args[key_arg_slice_start:]
+                elif key_arg_slice_stop:
+                    key = args[:key_arg_slice_stop]
+                else:
+                    key = args
+                
                 if kwds:
                     key += kwd_mark + tuple(sorted(kwds.items()))
                 try:
@@ -386,7 +395,16 @@ def wrapper(*args, **kwds):
 
             @wraps(user_function)
             def wrapper(*args, **kwds):
-                key = args
+                
+                if key_arg_slice_start and key_arg_slice_stop:
+                    key = args[key_arg_slice_start:key_arg_slice_stop]
+                elif key_arg_slice_start:
+                    key = args[key_arg_slice_start:]
+                elif key_arg_slice_stop:
+                    key = args[:key_arg_slice_stop]
+                else:
+                    key = args
+
                 if kwds:
                     key += kwd_mark + tuple(sorted(kwds.items()))
                 with lock:
diff --git a/test_functools32.py b/test_functools32.py
index b709f37..b9afc6b 100644
--- a/test_functools32.py
+++ b/test_functools32.py
@@ -637,6 +637,52 @@ def func(i):
             with self.assertRaises(IndexError):
                 func(15)
 
+    def test_lru_slice(self):
+        def orig(o, x, y):
+            return 3*x+y
+        f = functools.lru_cache(maxsize=20, key_arg_slice_start=1)(orig)
+        hits, misses, maxsize, currsize = f.cache_info()
+        self.assertEqual(maxsize, 20)
+        self.assertEqual(currsize, 0)
+        self.assertEqual(hits, 0)
+        self.assertEqual(misses, 0)
+
+        obj1 = "object1"
+        obj2 = "object2"
+        obj3 = "object3"
+        f(obj1, 1, 1)
+        f(obj2, 1, 1)
+        f(obj3, 1, 1)
+
+        hits, misses, maxsize, currsize = f.cache_info()
+        self.assertEqual(maxsize, 20)
+        self.assertEqual(currsize, 1)
+        self.assertEqual(hits, 2)
+        self.assertEqual(misses, 1)
+
+    def test_lru_slice_no_max(self):
+        def orig(o, x, y):
+            return 3*x+y
+        f = functools.lru_cache(maxsize=None, key_arg_slice_start=1)(orig)
+        hits, misses, maxsize, currsize = f.cache_info()
+        self.assertEqual(maxsize, None)
+        self.assertEqual(currsize, 0)
+        self.assertEqual(hits, 0)
+        self.assertEqual(misses, 0)
+
+        obj1 = "object1"
+        obj2 = "object2"
+        obj3 = "object3"
+        f(obj1, 1, 1)
+        f(obj2, 1, 1)
+        f(obj3, 1, 1)
+
+        hits, misses, maxsize, currsize = f.cache_info()
+        self.assertEqual(maxsize, None)
+        self.assertEqual(currsize, 1)
+        self.assertEqual(hits, 2)
+        self.assertEqual(misses, 1)
+
 class TestOrderedDict(unittest.TestCase):
     def test_move_to_end(self):
         od = OrderedDict.fromkeys('abcde')