Raise TypeError if formatter returns a non-string

Author: serhiy-storchaka

Lib/test/test_csv.py

@@ -535,7 +535,7 @@ def formatter(index, value):
     def test_write_formatter_errors(self):
         with self.assertRaisesRegex(TypeError, 'must be callable or None'):
             csv.writer(StringIO(), formatter='str')
-        with self.assertRaisesRegex(csv.Error, 'must return a string'):
+        with self.assertRaisesRegex(TypeError, 'must return a string'):
             self._write_test([1], '', formatter=lambda index, value: index)
         self._write_error_test(ZeroDivisionError, [1],
                                formatter=lambda index, value: 1/0)

Modules/_csv.c

@@ -1463,7 +1463,7 @@ csv_writerow_lock_held(PyObject *op, PyObject *seq)
                 str = PyObject_CallFunction(self->formatter, "nO",
                                             field_index, field);
                 if (str != NULL && !PyUnicode_Check(str)) {
-                    PyErr_Format(self->error_obj,
+                    PyErr_Format(PyExc_TypeError,
                                  "formatter must return a string, not %T", str);
                     Py_CLEAR(str);
                 }