bpo-21861: Improve _io classes __repr__

Instead of hardcoding the class name in the __repr__ string, resolve the
actuall one which makes the __repr__ more subclass friendly.

Author: Michal Kuffa

Lib/test/test_fileio.py

@@ -154,6 +154,27 @@ def test_none_args(self):
     def test_reject(self):
         self.assertRaises(TypeError, self.f.write, "Hello!")
 
+    def test_subclass_repr(self):
+        class CustomFileIO(self.FileIO):
+            pass
+
+        custom_file_io = CustomFileIO(TESTFN, 'w')
+
+        self.assertIn(
+            "CustomFileIO name=%r mode=%r closefd=True>" %
+            (custom_file_io.name, custom_file_io.mode),
+            repr(custom_file_io))
+
+        del custom_file_io.name
+        self.assertIn(
+            "CustomFileIO fd=%r mode=%r closefd=True>" %
+            (custom_file_io.fileno(), custom_file_io.mode),
+            repr(custom_file_io))
+
+        custom_file_io.close()
+        self.assertIn("CustomFileIO [closed]", repr(custom_file_io))
+
+
     def testRepr(self):
         self.assertEqual(repr(self.f),
                          "<%s.FileIO name=%r mode=%r closefd=True>" %

Lib/test/test_io.py

@@ -2630,6 +2630,30 @@ def test_repr(self):
         t.buffer.detach()
         repr(t)  # Should not raise an exception
 
+    def test_subclass_repr(self):
+        class SubTextIOWrapper(self.TextIOWrapper):
+            pass
+
+        clsname = 'SubTextIOWrapper'
+        raw = self.BytesIO("hello".encode("utf-8"))
+        b = self.BufferedReader(raw)
+        t = SubTextIOWrapper(b, encoding="utf-8")
+        self.assertRegex(repr(t),
+                         r"%s encoding='utf-8'>" % clsname)
+        raw.name = "dummy"
+        self.assertRegex(repr(t),
+                         r"%s name='dummy' encoding='utf-8'>" % clsname)
+        t.mode = "r"
+        self.assertRegex(repr(t),
+                         r"%s name='dummy' mode='r' encoding='utf-8'>" %
+                         clsname)
+        raw.name = b"dummy"
+        self.assertRegex(
+            repr(t),
+            r"%s name=b'dummy' mode='r' encoding='utf-8'>" % clsname)
+        t.buffer.detach()
+        repr(t)  # Should not raise an exception
+
     def test_recursive_repr(self):
         # Issue #25455
         raw = self.BytesIO()

Misc/NEWS.d/next/Core and Builtins/2019-07-14-13-12-40.bpo-21861.wxAr8e.rst

@@ -0,0 +1,2 @@
+Remove the hardcoded classes names from ``_io`` module classes' ``__repr__`` in
+favor of the actual object type name to make it more subclass friendly.

Modules/_io/fileio.c

@@ -1080,22 +1080,26 @@ fileio_repr(fileio *self)
     PyObject *nameobj, *res;
 
     if (self->fd < 0)
-        return PyUnicode_FromFormat("<_io.FileIO [closed]>");
+        return PyUnicode_FromFormat(
+            "<%s [closed]>",
+            Py_TYPE((PyObject *) self)->tp_name);
 
     if (_PyObject_LookupAttrId((PyObject *) self, &PyId_name, &nameobj) < 0) {
         return NULL;
     }
     if (nameobj == NULL) {
         res = PyUnicode_FromFormat(
-            "<_io.FileIO fd=%d mode='%s' closefd=%s>",
+            "<%s fd=%d mode='%s' closefd=%s>",
+            Py_TYPE((PyObject *) self)->tp_name,
             self->fd, mode_string(self), self->closefd ? "True" : "False");
     }
     else {
         int status = Py_ReprEnter((PyObject *)self);
         res = NULL;
         if (status == 0) {
             res = PyUnicode_FromFormat(
-                "<_io.FileIO name=%R mode='%s' closefd=%s>",
+                "<%s name=%R mode='%s' closefd=%s>",
+                Py_TYPE((PyObject *) self)->tp_name,
                 nameobj, mode_string(self), self->closefd ? "True" : "False");
             Py_ReprLeave((PyObject *)self);
         }

Modules/_io/textio.c

@@ -2886,7 +2886,7 @@ textiowrapper_repr(textio *self)
 
     CHECK_INITIALIZED(self);
 
-    res = PyUnicode_FromString("<_io.TextIOWrapper");
+    res = PyUnicode_FromFormat("<%s", Py_TYPE((PyObject *) self)->tp_name);
     if (res == NULL)
         return NULL;
 

Modules/_io/winconsoleio.c

@@ -1034,13 +1034,19 @@ static PyObject *
 winconsoleio_repr(winconsoleio *self)
 {
     if (self->handle == INVALID_HANDLE_VALUE)
-        return PyUnicode_FromFormat("<_io._WindowsConsoleIO [closed]>");
+        return PyUnicode_FromFormat(
+            "<%s [closed]>",
+            Py_TYPE((PyObject *) self)->tp_name);
 
     if (self->readable)
-        return PyUnicode_FromFormat("<_io._WindowsConsoleIO mode='rb' closefd=%s>",
+        return PyUnicode_FromFormat(
+            "<%s mode='rb' closefd=%s>",
+            Py_TYPE((PyObject *) self)->tp_name,
             self->closehandle ? "True" : "False");
     if (self->writable)
-        return PyUnicode_FromFormat("<_io._WindowsConsoleIO mode='wb' closefd=%s>",
+        return PyUnicode_FromFormat(
+            "<%s mode='wb' closefd=%s>",
+            Py_TYPE((PyObject *) self)->tp_name,
             self->closehandle ? "True" : "False");
 
     PyErr_SetString(PyExc_SystemError, "_WindowsConsoleIO has invalid mode");