From 5db331a561059afe7f7fedd75b4bc67550c988cd Mon Sep 17 00:00:00 2001
From: CF Bolz-Tereick <cfbolz@gmx.de>
Date: Wed, 21 Jan 2026 15:19:19 +0100
Subject: [PATCH] gh-144030: Add check that argument is callable to Python
 version of functools.lru_cache (#144031)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: AN Long <aisk@users.noreply.github.com>
---
 Lib/functools.py                                           | 3 +++
 Lib/test/test_functools.py                                 | 7 +++++++
 .../Library/2026-01-19-12-48-59.gh-issue-144030.7OK_gB.rst | 3 +++
 3 files changed, 13 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-01-19-12-48-59.gh-issue-144030.7OK_gB.rst

diff --git a/Lib/functools.py b/Lib/functools.py
index 075418b1605..59fc2a8fbf6 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -602,6 +602,9 @@ def lru_cache(maxsize=128, typed=False):
     return decorating_function
 
 def _lru_cache_wrapper(user_function, maxsize, typed, _CacheInfo):
+    if not callable(user_function):
+        raise TypeError("the first argument must be callable")
+
     # Constants shared by all lru cache instances:
     sentinel = object()          # unique object used to signal cache misses
     make_key = _make_key         # build a key from the function arguments
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index 94b46939713..3801a82a610 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -2157,6 +2157,13 @@ class TestLRU:
                 with self.assertRaises(RecursionError):
                     fib(support.exceeds_recursion_limit())
 
+    def test_lru_checks_arg_is_callable(self):
+        with self.assertRaisesRegex(
+            TypeError,
+            "the first argument must be callable",
+        ):
+            self.module.lru_cache(1)('hello')
+
 
 @py_functools.lru_cache()
 def py_cached_func(x, y):
diff --git a/Misc/NEWS.d/next/Library/2026-01-19-12-48-59.gh-issue-144030.7OK_gB.rst b/Misc/NEWS.d/next/Library/2026-01-19-12-48-59.gh-issue-144030.7OK_gB.rst
new file mode 100644
index 00000000000..ef3c0292540
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-01-19-12-48-59.gh-issue-144030.7OK_gB.rst
@@ -0,0 +1,3 @@
+The Python implementation of :func:`functools.lru_cache` differed from the
+default C implementation in that it did not check that its argument is
+callable. This discrepancy is now fixed and both raise a :exc:`TypeError`.