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Co-authored-by: Victor Stinner <vstinner@python.org>

Doc/c-api/weakref.rst

@@ -90,7 +90,7 @@ as much as it can.
 
 .. c:function:: int PyWeakref_IsDead(PyObject *ref)
 
-   Test if a weak reference, *ref*, is dead. Returns 1 if the reference is
+   Test if the weak reference *ref* is dead. Returns 1 if the reference is
    dead, 0 if it is alive, and -1 with an error set if *ref* is not a weak
    reference object.
 

Objects/weakrefobject.c

@@ -940,7 +940,7 @@ PyWeakref_IsDead(PyObject *ref)
         return -1;
     }
     if (!PyWeakref_Check(ref)) {
-        PyErr_SetString(PyExc_TypeError, "expected a weakref");
+        PyErr_Format(PyExc_TypeError, "expected a weakref, got %T", ref);
         return -1;
     }
     return _PyWeakref_IS_DEAD(ref);