fix: use in operator semantics in object_api::contains

include/pybind11/pytypes.h

@@ -2371,7 +2371,12 @@ args_proxy object_api<D>::operator*() const {
 template <typename D>
 template <typename T>
 bool object_api<D>::contains(T &&item) const {
-    return attr("__contains__")(std::forward<T>(item)).template cast<bool>();
+    const int result
+        = PySequence_Contains(derived().ptr(), object_or_cast(std::forward<T>(item)).ptr());
+    if (result == -1) {
+        throw error_already_set();
+    }
+    return result != 0;
 }
 
 template <typename D>

tests/test_pytypes.cpp

@@ -262,6 +262,8 @@ TEST_SUBMODULE(pytypes, m) {
           [](const py::anyset &set, const py::object &key) { return set.contains(key); });
     m.def("anyset_contains",
           [](const py::anyset &set, const char *key) { return set.contains(key); });
+    m.def("object_contains",
+          [](const py::object &obj, const py::object &item) { return obj.contains(item); });
     m.def("set_add", [](py::set &set, const py::object &key) { set.add(key); });
     m.def("set_clear", [](py::set &set) { set.clear(); });
 

tests/test_pytypes.py

@@ -108,6 +108,26 @@ def test_none(doc):
     assert doc(m.print_none) == "print_none(arg0: None) -> None"
 
 
+def test_object_contains():
+    class OnlyIter:
+        def __iter__(self):
+            return iter([1, 2])
+
+    class RaisingContains:
+        def __contains__(self, item):
+            raise ValueError("contains failed")
+
+    assert m.object_contains([1, 2], 1) is True
+    assert m.object_contains([1, 2], 3) is False
+    # The `in` operator falls back to iteration when there is no __contains__.
+    assert m.object_contains(OnlyIter(), 2) is True
+    assert m.object_contains(OnlyIter(), 3) is False
+    with pytest.raises(ValueError, match="contains failed"):
+        m.object_contains(RaisingContains(), 1)
+    with pytest.raises(TypeError):
+        m.object_contains(object(), 1)
+
+
 def test_set(capture, doc):
     s = m.get_set()
     assert isinstance(s, set)