improve error message on failing exec()

Cython/Utility/Builtins.c

@@ -140,8 +140,9 @@ static PyObject* __Pyx_PyExec3(PyObject* o, PyObject* globals, PyObject* locals)
         #else
         } else if (!PyString_Check(o)) {
         #endif
-            PyErr_SetString(PyExc_TypeError,
-                "exec: arg 1 must be string, bytes or code object");
+            PyErr_Format(PyExc_TypeError,
+                "exec: arg 1 must be string, bytes or code object, got %.200s",
+                Py_TYPE(o)->tp_name);
             goto bad;
         }
         #if PY_MAJOR_VERSION >= 3

tests/run/exectest.pyx

@@ -113,3 +113,11 @@ def test_encoding_unicode(d1, d2):
 def test_compile(d):
     c = compile(u"b = a+c", u"<string>", u"exec")
     exec c in d
+
+def exec_invalid_type(x):
+    """
+    >>> exec_invalid_type(42)
+    Traceback (most recent call last):
+    TypeError: exec: arg 1 must be string, bytes or code object, got int
+    """
+    exec x in {}