unicode parsing fix for encoding

Author: nanjekyejoannah

Include/object.h

@@ -105,6 +105,7 @@ whose size is determined when the object is allocated.
  */
 typedef struct _object {
     PyObject_HEAD
+    Py_ssize_t ob_bstate;
 } PyObject;
 
 typedef struct {

Lib/test/test_unicode.py

@@ -743,13 +743,13 @@ def __str__(self):
             self.assertRaises(
                 TypeError,
                 unicode,
-                u'decoding unicode is not supported',
+                u"'decode()' is not supported on Unicode in 3.x: convert the string to bytes.",
                 'utf-8',
                 'strict'
             )
 
         self.assertEqual(
-            unicode('strings are decoded to unicode', 'utf-8', 'strict'),
+            unicode("'decode()' is not supported on Unicode in 3.x: convert the string to bytes.", 'utf-8', 'strict'),
             u'strings are decoded to unicode'
         )
 

Objects/unicodeobject.c

@@ -1209,12 +1209,20 @@ PyObject *PyUnicode_FromEncodedObject(register PyObject *obj,
         return PyObject_Unicode(obj);
     }
 #else
+#endif
+    
     if (PyUnicode_Check(obj)) {
-        PyErr_SetString(PyExc_TypeError,
-                        "decoding Unicode is not supported");
-        return NULL;
+        if (encoding) {
+            obj->ob_bstate = BSTATE_BYTE;
+            if ((obj->ob_bstate == BSTATE_BYTE) &&
+                PyErr_WarnPy3k(
+                    "'decode()' is not supported on Unicode in 3.x: convert the string to bytes.", 1) < 0) {
+                return NULL;
+            }
+            return NULL;
+        }
+        return PyObject_Unicode(obj);
     }
-#endif
 
     /* Coerce object */
     if (PyString_Check(obj)) {
@@ -1304,8 +1312,14 @@ PyObject *PyUnicode_AsDecodedObject(PyObject *unicode,
         goto onError;
     }
 
-    if (PyErr_WarnPy3k("decoding Unicode is not supported in 3.x", 1) < 0)
-        goto onError;
+    if (PyString_CheckExact(unicode)) {
+        unicode->ob_bstate = BSTATE_BYTE;
+    }
+
+    if ((unicode->ob_bstate == BSTATE_BYTE) &&
+        PyErr_WarnPy3k("'decode()' is not supported on Unicode in 3.x: convert the string to bytes.", 1) < 0) {
+        return NULL;
+    }
 
     if (encoding == NULL)
         encoding = PyUnicode_GetDefaultEncoding();