gh-161233: Fix TypeError when timer=None was passed to cProfile.Profile

Lib/test/test_profiling/test_tracing_profiler.py

@@ -139,6 +139,20 @@ def timer():
         profiler.disable()
         profiler.clear()
 
+    def test_external_timer_is_none(self):
+        # gh-161233
+        def work():
+            pass
+
+        for kwargs in ({}, {'timer': None}):
+            with self.subTest(kwargs=kwargs):
+                profiler = cProfile.Profile(**kwargs)
+                profiler.enable()
+                with support.catch_unraisable_exception() as cm:
+                    work()
+                    self.assertIsNone(cm.unraisable)
+                profiler.disable()
+
     def test_profile_enable_disable(self):
         prof = self.profilerclass()
         # Make sure we clean ourselves up if the test fails for some reason.

Misc/NEWS.d/next/Library/2026-11-03-10-33-33.gh-issue-161233._9VrfL.rst

@@ -0,0 +1,2 @@
+Fix unraisable :exc:`TypeError` when ``None`` was passed as a *timer* to
+:class:`cProfile.Profile <profile.Profile>`.

Modules/_lsprof.c

@@ -92,6 +92,7 @@ _lsprof_get_state(PyObject *module)
 
 static PyTime_t CallExternalTimer(ProfilerObject *pObj)
 {
+    assert(pObj->externalTimer != NULL && pObj->externalTimer != Py_None);
     PyObject *o = _PyObject_CallNoArgs(pObj->externalTimer);
 
     if (o == NULL) {
@@ -1031,6 +1032,9 @@ profiler_init_impl(ProfilerObject *self, PyObject *timer, double timeunit,
     if (setSubcalls(self, subcalls) < 0 || setBuiltins(self, builtins) < 0) {
         return -1;
     }
+    if (timer == Py_None) {
+        timer = NULL;
+    }
     self->externalTimerUnit = timeunit;
     Py_XSETREF(self->externalTimer, Py_XNewRef(timer));
     self->tool_id = PY_MONITORING_PROFILER_ID;