bpo-29838: Add asserts for checking results of sq_length and mq_length slots. (#700)

Negative result should be returned only when an error is set.

1 files changed, 3 insertions, 1 deletions

diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index 8ae2303..60d1b7c 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -1479,8 +1479,10 @@ builtin_len(PyObject *module, PyObject *obj)
     Py_ssize_t res;
 
     res = PyObject_Size(obj);
-    if (res < 0 && PyErr_Occurred())
+    if (res < 0) {
+        assert(PyErr_Occurred());
         return NULL;
+    }
     return PyLong_FromSsize_t(res);
 }