Fail on passing py::object with wrong Python type to py::object subclass using PYBIND11_OBJECT macro

Author: YannickJadoul

include/pybind11/pytypes.h

@@ -798,11 +798,16 @@ PYBIND11_NAMESPACE_END(detail)
     : Parent(check_(o) ? o.release().ptr() : ConvertFun(o.ptr()), stolen_t{}) \
     { if (!m_ptr) throw error_already_set(); }
 
+#define PYBIND11_OBJECT_CHECK_FAILED(Name, o) \
+    type_error("Object of type '" + std::string(Py_TYPE(o.ptr())->tp_name) + "' is not an instance of '" #Name "'")
+
 #define PYBIND11_OBJECT(Name, Parent, CheckFun) \
     PYBIND11_OBJECT_COMMON(Name, Parent, CheckFun) \
     /* This is deliberately not 'explicit' to allow implicit conversion from object: */ \
-    Name(const object &o) : Parent(o) { } \
-    Name(object &&o) : Parent(std::move(o)) { }
+    Name(const object &o) : Parent(o) \
+    { if (o && !check_(o)) throw PYBIND11_OBJECT_CHECK_FAILED(Name, o); } \
+    Name(object &&o) : Parent(std::move(o)) \
+    { if (o && !check_(o)) throw PYBIND11_OBJECT_CHECK_FAILED(Name, o); }
 
 #define PYBIND11_OBJECT_DEFAULT(Name, Parent, CheckFun) \
     PYBIND11_OBJECT(Name, Parent, CheckFun) \

tests/test_pytypes.cpp

@@ -240,6 +240,19 @@ TEST_SUBMODULE(pytypes, m) {
         );
     });
 
+    m.def("nonconverting_constructor", [](std::string type, py::object value) -> py::object {
+        if (type == "bytes") {
+            return py::bytes(value);
+        }
+        else if (type == "none") {
+            return py::none(value);
+        }
+        else if (type == "ellipsis") {
+            return py::ellipsis(value);
+        }
+        throw std::runtime_error("Invalid type");
+    });
+
     m.def("get_implicit_casting", []() {
         py::dict d;
         d["char*_i1"] = "abc";

tests/test_pytypes.py

@@ -225,6 +225,18 @@ def test_constructors():
     for k in noconv2:
         assert noconv2[k] is expected[k]
 
+    type_error_tests = [
+        ("bytes", range(10)),
+        ("none", 42),
+        ("ellipsis", 42),
+    ]
+    for t, v in type_error_tests:
+        with pytest.raises(TypeError) as excinfo:
+            m.nonconverting_constructor(t, v)
+        expected_error = "Object of type '{}' is not an instance of '{}'".format(
+            type(v).__name__, t)
+        assert str(excinfo.value) == expected_error
+
 
 def test_implicit_casting():
     """Tests implicit casting when assigning or appending to dicts and lists."""