bpo-43753: Add Py_Is() and Py_IsNone() functions (GH-25227)

Add the Py_Is(x, y) function to test if the 'x' object is the 'y'
object, the same as "x is y" in Python. Add also the Py_IsNone(),
Py_IsTrue(), Py_IsFalse() functions to test if an object is,
respectively, the None singleton, the True singleton or the False
singleton.

Modules/_testcapimodule.c

@@ -5401,32 +5401,98 @@ test_set_type_size(PyObject *self, PyObject *Py_UNUSED(ignored))
 }
 
 
-// Test Py_NewRef() and Py_XNewRef() functions
+#define TEST_REFCOUNT() \
+    do { \
+        PyObject *obj = PyList_New(0); \
+        if (obj == NULL) { \
+            return NULL; \
+        } \
+        assert(Py_REFCNT(obj) == 1); \
+        \
+        /* test Py_NewRef() */ \
+        PyObject *ref = Py_NewRef(obj); \
+        assert(ref == obj); \
+        assert(Py_REFCNT(obj) == 2); \
+        Py_DECREF(ref); \
+        \
+        /* test Py_XNewRef() */ \
+        PyObject *xref = Py_XNewRef(obj); \
+        assert(xref == obj); \
+        assert(Py_REFCNT(obj) == 2); \
+        Py_DECREF(xref); \
+        \
+        assert(Py_XNewRef(NULL) == NULL); \
+        \
+        Py_DECREF(obj); \
+        Py_RETURN_NONE; \
+    } while (0) \
+
+
+// Test Py_NewRef() and Py_XNewRef() macros
 static PyObject*
-test_refcount(PyObject *self, PyObject *Py_UNUSED(ignored))
+test_refcount_macros(PyObject *self, PyObject *Py_UNUSED(ignored))
 {
-    PyObject *obj = PyList_New(0);
-    if (obj == NULL) {
-        return NULL;
-    }
-    assert(Py_REFCNT(obj) == 1);
+    TEST_REFCOUNT();
+}
 
-    // Test Py_NewRef()
-    PyObject *ref = Py_NewRef(obj);
-    assert(ref == obj);
-    assert(Py_REFCNT(obj) == 2);
-    Py_DECREF(ref);
+#undef Py_NewRef
+#undef Py_XNewRef
 
-    // Test Py_XNewRef()
-    PyObject *xref = Py_XNewRef(obj);
-    assert(xref == obj);
-    assert(Py_REFCNT(obj) == 2);
-    Py_DECREF(xref);
+// Test Py_NewRef() and Py_XNewRef() functions, after undefining macros.
+static PyObject*
+test_refcount_funcs(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    TEST_REFCOUNT();
+}
 
-    assert(Py_XNewRef(NULL) == NULL);
 
-    Py_DECREF(obj);
-    Py_RETURN_NONE;
+// Test Py_Is() function
+#define TEST_PY_IS() \
+    do { \
+        PyObject *o_none = Py_None; \
+        PyObject *o_true = Py_True; \
+        PyObject *o_false = Py_False; \
+        PyObject *obj = PyList_New(0); \
+        if (obj == NULL) { \
+            return NULL; \
+        } \
+        \
+        /* test Py_Is() */ \
+        assert(Py_Is(obj, obj)); \
+        assert(!Py_Is(obj, o_none)); \
+        \
+        /* test Py_None */ \
+        assert(Py_Is(o_none, o_none)); \
+        assert(!Py_Is(obj, o_none)); \
+        \
+        /* test Py_True */ \
+        assert(Py_Is(o_true, o_true)); \
+        assert(!Py_Is(o_false, o_true)); \
+        assert(!Py_Is(obj, o_true)); \
+        \
+        /* test Py_False */ \
+        assert(Py_Is(o_false, o_false)); \
+        assert(!Py_Is(o_true, o_false)); \
+        assert(!Py_Is(obj, o_false)); \
+        \
+        Py_DECREF(obj); \
+        Py_RETURN_NONE; \
+    } while (0)
+
+// Test Py_Is() macro
+static PyObject*
+test_py_is_macros(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    TEST_PY_IS();
+}
+
+#undef Py_Is
+
+// Test Py_Is() function, after undefining its macro.
+static PyObject*
+test_py_is_funcs(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    TEST_PY_IS();
 }
 
 
@@ -5716,7 +5782,10 @@ static PyMethodDef TestMethods[] = {
     {"pynumber_tobase", pynumber_tobase, METH_VARARGS},
     {"without_gc", without_gc, METH_O},
     {"test_set_type_size", test_set_type_size, METH_NOARGS},
-    {"test_refcount", test_refcount, METH_NOARGS},
+    {"test_refcount_macros", test_refcount_macros, METH_NOARGS},
+    {"test_refcount_funcs", test_refcount_funcs, METH_NOARGS},
+    {"test_py_is_macros", test_py_is_macros, METH_NOARGS},
+    {"test_py_is_funcs", test_py_is_funcs, METH_NOARGS},
     {"fatal_error", test_fatal_error, METH_VARARGS,
      PyDoc_STR("fatal_error(message, release_gil=False): call Py_FatalError(message)")},
     {NULL, NULL} /* sentinel */