bpo-24234: Implement bytes.__bytes__ (GH-27901)

Author: corona10

Doc/whatsnew/3.11.rst

@@ -169,6 +169,14 @@ Other Language Changes
   (Contributed by Serhiy Storchaka in :issue:`12022`.)
 
 
+Other CPython Implementation Changes
+====================================
+
+* Special methods :meth:`complex.__complex__` and :meth:`bytes.__bytes__` are implemented to
+  support :class:`typing.SupportsComplex` and :class:`typing.SupportsBytes` protocols.
+  (Contributed by Mark Dickinson and Dong-hee Na in :issue:`24234`.)
+
+
 New Modules
 ===========
 

Lib/test/test_bytes.py

@@ -981,6 +981,18 @@ def test_sq_item(self):
 class BytesTest(BaseBytesTest, unittest.TestCase):
     type2test = bytes
 
+    def test__bytes__(self):
+        foo = b'foo'
+        self.assertEqual(foo.__bytes__(), foo)
+        self.assertEqual(type(foo.__bytes__()), self.type2test)
+
+        class bytes_subclass(bytes):
+            pass
+
+        bar = bytes_subclass(b'bar')
+        self.assertEqual(bar.__bytes__(), bar)
+        self.assertEqual(type(bar.__bytes__()), self.type2test)
+
     def test_getitem_error(self):
         b = b'python'
         msg = "byte indices must be integers or slices"

Lib/test/test_typing.py

@@ -1543,11 +1543,11 @@ def __complex__(self):
 
     def test_supports_bytes(self):
 
-        # Note: bytes itself doesn't have __bytes__.
         class B:
             def __bytes__(self):
                 return b''
 
+        self.assertIsSubclass(bytes, typing.SupportsBytes)
         self.assertIsSubclass(B, typing.SupportsBytes)
         self.assertNotIsSubclass(str, typing.SupportsBytes)
 

Misc/NEWS.d/next/Core and Builtins/2021-08-23-10-36-55.bpo-24234.MGVUQi.rst

@@ -0,0 +1,3 @@
+Implement the :meth:`__bytes__` special method on the :class:`bytes` type,
+so a bytes object ``b``  passes an ``isinstance(b, typing.SupportsBytes)``
+check.

Objects/bytesobject.c

@@ -1687,6 +1687,25 @@ static PyBufferProcs bytes_as_buffer = {
 };
 
 
+/*[clinic input]
+bytes.__bytes__
+Convert this value to exact type bytes.
+[clinic start generated code]*/
+
+static PyObject *
+bytes___bytes___impl(PyBytesObject *self)
+/*[clinic end generated code: output=63a306a9bc0caac5 input=34ec5ddba98bd6bb]*/
+{
+    if (PyBytes_CheckExact(self)) {
+        Py_INCREF(self);
+        return (PyObject *)self;
+    }
+    else {
+        return PyBytes_FromString(self->ob_sval);
+    }
+}
+
+
 #define LEFTSTRIP 0
 #define RIGHTSTRIP 1
 #define BOTHSTRIP 2
@@ -2474,6 +2493,7 @@ bytes_getnewargs(PyBytesObject *v, PyObject *Py_UNUSED(ignored))
 static PyMethodDef
 bytes_methods[] = {
     {"__getnewargs__",          (PyCFunction)bytes_getnewargs,  METH_NOARGS},
+    BYTES___BYTES___METHODDEF
     {"capitalize", stringlib_capitalize, METH_NOARGS,
      _Py_capitalize__doc__},
     STRINGLIB_CENTER_METHODDEF

Objects/clinic/bytesobject.c.h

@@ -2179,7 +2179,6 @@ def __repr__(self):
 __abs__
 __add__
 __and__
-__bytes__
 __call__
 __delitem__
 __divmod__