Allow "".decode()

from_cpython/Objects/stringobject.c

@@ -206,3 +206,65 @@ string_splitlines(PyStringObject *self, PyObject *args)
         keepends
     );
 }
+
+PyObject *PyString_AsDecodedObject(PyObject *str,
+                                   const char *encoding,
+                                   const char *errors)
+{
+    PyObject *v;
+
+    if (!PyString_Check(str)) {
+        PyErr_BadArgument();
+        goto onError;
+    }
+
+    if (encoding == NULL) {
+#ifdef Py_USING_UNICODE
+        encoding = PyUnicode_GetDefaultEncoding();
+#else
+        PyErr_SetString(PyExc_ValueError, "no encoding specified");
+        goto onError;
+#endif
+    }
+
+    /* Decode via the codec registry */
+    v = PyCodec_Decode(str, encoding, errors);
+    if (v == NULL)
+        goto onError;
+
+    return v;
+
+ onError:
+    return NULL;
+}
+
+PyObject *PyString_AsEncodedObject(PyObject *str,
+                                   const char *encoding,
+                                   const char *errors)
+{
+    PyObject *v;
+
+    if (!PyString_Check(str)) {
+        PyErr_BadArgument();
+        goto onError;
+    }
+
+    if (encoding == NULL) {
+#ifdef Py_USING_UNICODE
+        encoding = PyUnicode_GetDefaultEncoding();
+#else
+        PyErr_SetString(PyExc_ValueError, "no encoding specified");
+        goto onError;
+#endif
+    }
+
+    /* Encode via the codec registry */
+    v = PyCodec_Encode(str, encoding, errors);
+    if (v == NULL)
+        goto onError;
+
+    return v;
+
+ onError:
+    return NULL;
+}

src/runtime/str.cpp

@@ -2194,8 +2194,8 @@ Box* strDecode(BoxedString* self, Box* encoding, Box* error) {
     if (error_str && !isSubclass(error_str->cls, str_cls))
         raiseExcHelper(TypeError, "decode() argument 2 must be string, not '%s'", getTypeName(error_str));
 
-    Box* result
-        = PyCodec_Decode(self, encoding_str ? encoding_str->data() : NULL, error_str ? error_str->data() : NULL);
+    Box* result = PyString_AsDecodedObject(self, encoding_str ? encoding_str->data() : NULL,
+                                           error_str ? error_str->data() : NULL);
     checkAndThrowCAPIException();
     return result;
 }
@@ -2219,7 +2219,7 @@ Box* strEncode(BoxedString* self, Box* encoding, Box* error) {
     if (error_str && !isSubclass(error_str->cls, str_cls))
         raiseExcHelper(TypeError, "encode() argument 2 must be string, not '%s'", getTypeName(error_str));
 
-    Box* result = PyCodec_Encode(self, encoding_str ? encoding_str->data() : PyUnicode_GetDefaultEncoding(),
+    Box* result = PyString_AsEncodedObject(self, encoding_str ? encoding_str->data() : PyUnicode_GetDefaultEncoding(),
                                  error_str ? error_str->data() : NULL);
     checkAndThrowCAPIException();
     return result;

test/tests/str_encode_decode.py

@@ -7,3 +7,7 @@ test("hello world", "hex")
 test("hello world", "base64")
 test("\r\n\\", "string-escape")
 
+"".encode()
+"".decode()
+u"".encode()
+u"".decode()