gh-110782: Fix crash when TypeVar is constructed with keyword args (#110784)

3 files changed, 28 insertions, 18 deletions

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 66812f3..1a1e0a25 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -554,6 +554,12 @@ class TypeVarTests(BaseTestCase):
                     vals[x] = cls(str(x))
                 del vals
 
+    def test_constructor(self):
+        T = TypeVar(name="T")
+        self.assertEqual(T.__name__, "T")
+        self.assertEqual(T.__constraints__, ())
+        self.assertIs(T.__bound__, None)
+
 
 def template_replace(templates: list[str], replacements: dict[str, list[str]]) -> list[tuple[str]]:
     """Renders templates with possible combinations of replacements.
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-10-12-15-03-24.gh-issue-110782.EqzIzi.rst b/Misc/NEWS.d/next/Core and Builtins/2023-10-12-15-03-24.gh-issue-110782.EqzIzi.rst
new file mode 100644
index 0000000..6eddcc0
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-10-12-15-03-24.gh-issue-110782.EqzIzi.rst
@@ -0,0 +1,2 @@
+Fix crash when :class:`typing.TypeVar` is constructed with a keyword
+argument. Patch by Jelle Zijlstra.
diff --git a/Objects/typevarobject.c b/Objects/typevarobject.c
index 73cdf48..8a20b23 100644
--- a/Objects/typevarobject.c
+++ b/Objects/typevarobject.c
@@ -364,24 +364,26 @@ typevar_new_impl(PyTypeObject *type, PyObject *name, PyObject *constraints,
         }
     }
 
-    if (!PyTuple_CheckExact(constraints)) {
-        PyErr_SetString(PyExc_TypeError,
-                        "constraints must be a tuple");
-        return NULL;
-    }
-    Py_ssize_t n_constraints = PyTuple_GET_SIZE(constraints);
-    if (n_constraints == 1) {
-        PyErr_SetString(PyExc_TypeError,
-                        "A single constraint is not allowed");
-        Py_XDECREF(bound);
-        return NULL;
-    } else if (n_constraints == 0) {
-        constraints = NULL;
-    } else if (bound != NULL) {
-        PyErr_SetString(PyExc_TypeError,
-                        "Constraints cannot be combined with bound=...");
-        Py_XDECREF(bound);
-        return NULL;
+    if (constraints != NULL) {
+        if (!PyTuple_CheckExact(constraints)) {
+            PyErr_SetString(PyExc_TypeError,
+                            "constraints must be a tuple");
+            return NULL;
+        }
+        Py_ssize_t n_constraints = PyTuple_GET_SIZE(constraints);
+        if (n_constraints == 1) {
+            PyErr_SetString(PyExc_TypeError,
+                            "A single constraint is not allowed");
+            Py_XDECREF(bound);
+            return NULL;
+        } else if (n_constraints == 0) {
+            constraints = NULL;
+        } else if (bound != NULL) {
+            PyErr_SetString(PyExc_TypeError,
+                            "Constraints cannot be combined with bound=...");
+            Py_XDECREF(bound);
+            return NULL;
+        }
     }
     PyObject *module = caller();
     if (module == NULL) {