- A new type object, 'string', is added. This is a common base type

  for 'str' and 'unicode', and can be used instead of
  types.StringTypes, e.g. to test whether something is "a string":
  isinstance(x, string) is True for Unicode and 8-bit strings.  This
  is an abstract base class and cannot be instantiated directly.

3 files changed, 61 insertions, 2 deletions

diff --git a/Objects/object.c b/Objects/object.c
index 1bd8db9..b1bf2c3 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -1779,6 +1779,9 @@ _Py_ReadyTypes(void)
 	if (PyType_Ready(&PyBool_Type) < 0)
 		Py_FatalError("Can't initialize 'bool'");
 
+	if (PyType_Ready(&PyString_Type) < 0)
+		Py_FatalError("Can't initialize 'str'");
+
 	if (PyType_Ready(&PyList_Type) < 0)
 		Py_FatalError("Can't initialize 'list'");
 
diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index 668668c..27b3af4 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -2855,6 +2855,60 @@ str_subtype_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 	return pnew;
 }
 
+static PyObject *
+basestring_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
+{
+	PyErr_SetString(PyExc_TypeError,
+			"The string type cannot be instantiated");
+	return NULL;
+}
+
+static char basestring_doc[] =
+"Type string cannot be instantiated; it is the base for str and unicode.";
+
+PyTypeObject PyBaseString_Type = {
+	PyObject_HEAD_INIT(&PyType_Type)
+	0,
+	"string",
+	0,
+	0,
+ 	0,			 		/* tp_dealloc */
+	0,			 		/* tp_print */
+	0,					/* tp_getattr */
+	0,					/* tp_setattr */
+	0,					/* tp_compare */
+	0,		 			/* tp_repr */
+	0,					/* tp_as_number */
+	0,					/* tp_as_sequence */
+	0,					/* tp_as_mapping */
+	0,		 			/* tp_hash */
+	0,					/* tp_call */
+	0,					/* tp_str */
+	0,					/* tp_getattro */
+	0,					/* tp_setattro */
+	0,					/* tp_as_buffer */
+	Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /* tp_flags */
+	basestring_doc,				/* tp_doc */
+	0,					/* tp_traverse */
+	0,					/* tp_clear */
+	0,					/* tp_richcompare */
+	0,					/* tp_weaklistoffset */
+	0,					/* tp_iter */
+	0,					/* tp_iternext */
+	0,					/* tp_methods */
+	0,					/* tp_members */
+	0,					/* tp_getset */
+	&PyBaseObject_Type,			/* tp_base */
+	0,					/* tp_dict */
+	0,					/* tp_descr_get */
+	0,					/* tp_descr_set */
+	0,					/* tp_dictoffset */
+	0,					/* tp_init */
+	0,					/* tp_alloc */
+	basestring_new,				/* tp_new */
+	0,		                	/* tp_free */
+};
+
 static char string_doc[] =
 "str(object) -> string\n\
 \n\
@@ -2893,7 +2947,7 @@ PyTypeObject PyString_Type = {
 	string_methods,				/* tp_methods */
 	0,					/* tp_members */
 	0,					/* tp_getset */
-	0,					/* tp_base */
+	&PyBaseString_Type,			/* tp_base */
 	0,					/* tp_dict */
 	0,					/* tp_descr_get */
 	0,					/* tp_descr_set */
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 5cc8455..0ac4941 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -5835,7 +5835,7 @@ PyTypeObject PyUnicode_Type = {
     unicode_methods,			/* tp_methods */
     0,					/* tp_members */
     0,					/* tp_getset */
-    0,					/* tp_base */
+    &PyBaseString_Type,			/* tp_base */
     0,					/* tp_dict */
     0,					/* tp_descr_get */
     0,					/* tp_descr_set */
@@ -5859,6 +5859,8 @@ void _PyUnicode_Init(void)
     strcpy(unicode_default_encoding, "ascii");
     for (i = 0; i < 256; i++)
 	unicode_latin1[i] = NULL;
+    if (PyType_Ready(&PyUnicode_Type) < 0)
+	Py_FatalError("Can't initialize 'unicode'");
 }
 
 /* Finalize the Unicode implementation */