Issue #25447: Copying the lru_cache() wrapper object now always works,

independedly from the type of the wrapped object (by returning the original
object unchanged).

Lib/test/test_functools.py

@@ -1262,14 +1262,24 @@ class TestLRU:
 
     def test_copy(self):
         cls = self.__class__
-        for f in cls.cached_func[0], cls.cached_meth, cls.cached_staticmeth:
+        def orig(x, y):
+            return 3 * x + y
+        part = self.module.partial(orig, 2)
+        funcs = (cls.cached_func[0], cls.cached_meth, cls.cached_staticmeth,
+                 self.module.lru_cache(2)(part))
+        for f in funcs:
             with self.subTest(func=f):
                 f_copy = copy.copy(f)
                 self.assertIs(f_copy, f)
 
     def test_deepcopy(self):
         cls = self.__class__
-        for f in cls.cached_func[0], cls.cached_meth, cls.cached_staticmeth:
+        def orig(x, y):
+            return 3 * x + y
+        part = self.module.partial(orig, 2)
+        funcs = (cls.cached_func[0], cls.cached_meth, cls.cached_staticmeth,
+                 self.module.lru_cache(2)(part))
+        for f in funcs:
             with self.subTest(func=f):
                 f_copy = copy.deepcopy(f)
                 self.assertIs(f_copy, f)

Misc/NEWS

@@ -123,6 +123,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #25447: Copying the lru_cache() wrapper object now always works,
+  independedly from the type of the wrapped object (by returning the original
+  object unchanged).
+
 - Issue #25768: Have the functions in compileall return booleans instead of
   ints and add proper documentation and tests for the return values.
 

Modules/_functoolsmodule.c

@@ -1053,6 +1053,20 @@ lru_cache_reduce(PyObject *self, PyObject *unused)
     return PyObject_GetAttrString(self, "__qualname__");
 }
 
+static PyObject *
+lru_cache_copy(PyObject *self, PyObject *unused)
+{
+    Py_INCREF(self);
+    return self;
+}
+
+static PyObject *
+lru_cache_deepcopy(PyObject *self, PyObject *unused)
+{
+    Py_INCREF(self);
+    return self;
+}
+
 static int
 lru_cache_tp_traverse(lru_cache_object *self, visitproc visit, void *arg)
 {
@@ -1104,6 +1118,8 @@ static PyMethodDef lru_cache_methods[] = {
     {"cache_info", (PyCFunction)lru_cache_cache_info, METH_NOARGS},
     {"cache_clear", (PyCFunction)lru_cache_cache_clear, METH_NOARGS},
     {"__reduce__", (PyCFunction)lru_cache_reduce, METH_NOARGS},
+    {"__copy__", (PyCFunction)lru_cache_copy, METH_VARARGS},
+    {"__deepcopy__", (PyCFunction)lru_cache_deepcopy, METH_VARARGS},
     {NULL}
 };