gh-102500: Implement PEP 688

Include/internal/pycore_global_strings.h

@@ -81,6 +81,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(__await__)
         STRUCT_FOR_ID(__bases__)
         STRUCT_FOR_ID(__bool__)
+        STRUCT_FOR_ID(__buffer__)
         STRUCT_FOR_ID(__build_class__)
         STRUCT_FOR_ID(__builtins__)
         STRUCT_FOR_ID(__bytes__)
@@ -180,6 +181,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(__rdivmod__)
         STRUCT_FOR_ID(__reduce__)
         STRUCT_FOR_ID(__reduce_ex__)
+        STRUCT_FOR_ID(__release_buffer__)
         STRUCT_FOR_ID(__repr__)
         STRUCT_FOR_ID(__reversed__)
         STRUCT_FOR_ID(__rfloordiv__)

Include/internal/pycore_memoryobject.h

@@ -0,0 +1,17 @@
+#ifndef Py_INTERNAL_MEMORYOBJECT_H
+#define Py_INTERNAL_MEMORYOBJECT_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+PyObject *
+PyMemoryView_FromObjectAndFlags(PyObject *v, int flags);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_MEMORYOBJECT_H */

Include/internal/pycore_typeobject.h

@@ -98,6 +98,8 @@ _Py_type_getattro(PyTypeObject *type, PyObject *name);
 PyObject *_Py_slot_tp_getattro(PyObject *self, PyObject *name);
 PyObject *_Py_slot_tp_getattr_hook(PyObject *self, PyObject *name);
 
+PyAPI_DATA(PyTypeObject) _PyBufferWrapper_Type;
+
 #ifdef __cplusplus
 }
 #endif

Include/pybuffer.h

@@ -104,7 +104,7 @@ PyAPI_FUNC(void) PyBuffer_Release(Py_buffer *view);
 /* Maximum number of dimensions */
 #define PyBUF_MAX_NDIM 64
 
-/* Flags for getting buffers */
+/* Flags for getting buffers. Keep these in sync with inspect.BufferFlags. */
 #define PyBUF_SIMPLE 0
 #define PyBUF_WRITABLE 0x0001
 

Lib/_collections_abc.py

@@ -49,7 +49,7 @@ def _f(): pass
            "Mapping", "MutableMapping",
            "MappingView", "KeysView", "ItemsView", "ValuesView",
            "Sequence", "MutableSequence",
-           "ByteString",
+           "ByteString", "Buffer",
            ]
 
 # This module has been renamed from collections.abc to _collections_abc to
@@ -439,6 +439,21 @@ def __subclasshook__(cls, C):
         return NotImplemented
 
 
+class Buffer(metaclass=ABCMeta):
+
+    __slots__ = ()
+
+    @abstractmethod
+    def __buffer__(self, flags: int, /) -> memoryview:
+        raise NotImplementedError
+
+    @classmethod
+    def __subclasshook__(cls, C):
+        if cls is Buffer:
+            return _check_methods(C, "__buffer__")
+        return NotImplemented
+
+
 class _CallableGenericAlias(GenericAlias):
     """ Represent `Callable[argtypes, resulttype]`.
 

Lib/inspect.py

@@ -39,6 +39,7 @@
     "Attribute",
     "BlockFinder",
     "BoundArguments",
+    "BufferFlags",
     "CORO_CLOSED",
     "CORO_CREATED",
     "CORO_RUNNING",
@@ -3296,6 +3297,28 @@ def signature(obj, *, follow_wrapped=True, globals=None, locals=None, eval_str=F
                                    globals=globals, locals=locals, eval_str=eval_str)
 
 
+class BufferFlags(enum.IntFlag):
+    SIMPLE = 0x0
+    WRITABLE = 0x1
+    FORMAT = 0x4
+    ND = 0x8
+    STRIDES = 0x10 | ND
+    C_CONTIGUOUS = 0x20 | STRIDES
+    F_CONTIGUOUS = 0x40 | STRIDES
+    ANY_CONTIGUOUS = 0x80 | STRIDES
+    INDIRECT = 0x100 | STRIDES
+    CONTIG = ND | WRITABLE
+    CONTIG_RO = ND
+    STRIDED = STRIDES | WRITABLE
+    STRIDED_RO = STRIDES
+    RECORDS = STRIDES | WRITABLE | FORMAT
+    RECORDS_RO = STRIDES | FORMAT
+    FULL = INDIRECT | WRITABLE | FORMAT
+    FULL_RO = INDIRECT | FORMAT
+    READ = 0x100
+    WRITE = 0x200
+
+
 def _main():
     """ Logic for inspecting an object given at command line """
     import argparse

Lib/test/test_buffer.py

@@ -4436,5 +4436,95 @@ def test_pybuffer_size_from_format(self):
                              struct.calcsize(format))
 
 
+class TestPythonBufferProtocol(unittest.TestCase):
+    def test_basic(self):
+        class MyBuffer:
+            def __buffer__(self, flags):
+                return memoryview(b"hello")
+
+        mv = memoryview(MyBuffer())
+        self.assertEqual(mv.tobytes(), b"hello")
+        self.assertEqual(bytes(MyBuffer()), b"hello")
+
+    def test_bad_buffer_method(self):
+        class MustReturnMV:
+            def __buffer__(self, flags):
+                return 42
+
+        self.assertRaises(TypeError, memoryview, MustReturnMV())
+
+        class WrongArity:
+            def __buffer__(self):
+                return memoryview(b"hello")
+
+        self.assertRaises(TypeError, memoryview, WrongArity())
+
+    def test_release_buffer(self):
+        class WhatToRelease:
+            def __init__(self):
+                self.held = False
+                self.ba = bytearray(b"hello")
+            def __buffer__(self, flags):
+                if self.held:
+                    raise TypeError("already held")
+                self.held = True
+                return memoryview(self.ba)
+            def __release_buffer__(self, buffer):
+                self.held = False
+
+        wr = WhatToRelease()
+        self.assertFalse(wr.held)
+        with memoryview(wr) as mv:
+            self.assertTrue(wr.held)
+            self.assertEqual(mv.tobytes(), b"hello")
+        self.assertFalse(wr.held)
+
+    def test_same_buffer_returned(self):
+        class WhatToRelease:
+            def __init__(self):
+                self.held = False
+                self.ba = bytearray(b"hello")
+                self.created_mv = None
+            def __buffer__(self, flags):
+                if self.held:
+                    raise TypeError("already held")
+                self.held = True
+                self.created_mv = memoryview(self.ba)
+                return self.created_mv
+            def __release_buffer__(self, buffer):
+                assert buffer is self.created_mv
+                self.held = False
+
+        wr = WhatToRelease()
+        self.assertFalse(wr.held)
+        with memoryview(wr) as mv:
+            self.assertTrue(wr.held)
+            self.assertEqual(mv.tobytes(), b"hello")
+        self.assertFalse(wr.held)
+
+    def test_call_builtins(self):
+        ba = bytearray(b"hello")
+        mv = ba.__buffer__(0)
+        self.assertEqual(mv.tobytes(), b"hello")
+        ba.__release_buffer__(mv)
+
+    @unittest.skipIf(_testcapi is None, "requires _testcapi")
+    def test_c_buffer(self):
+        buf = _testcapi.testBuf()
+        self.assertEqual(buf.references, 0)
+        mv = buf.__buffer__(0)
+        self.assertIsInstance(mv, memoryview)
+        self.assertEqual(mv.tobytes(), b"test")
+        self.assertEqual(buf.references, 1)
+        buf.__release_buffer__(mv)
+        self.assertEqual(buf.references, 0)
+        with self.assertRaises(ValueError):
+            mv.tobytes()
+        # Calling it again doesn't cause issues
+        with self.assertRaises(ValueError):
+            buf.__release_buffer__(mv)
+        self.assertEqual(buf.references, 0)
+
+
 if __name__ == "__main__":
     unittest.main()

Lib/test/test_collections.py

@@ -25,7 +25,7 @@
 from collections.abc import Set, MutableSet
 from collections.abc import Mapping, MutableMapping, KeysView, ItemsView, ValuesView
 from collections.abc import Sequence, MutableSequence
-from collections.abc import ByteString
+from collections.abc import ByteString, Buffer
 
 
 class TestUserObjects(unittest.TestCase):
@@ -1949,6 +1949,15 @@ def test_ByteString(self):
         self.assertFalse(issubclass(memoryview, ByteString))
         self.validate_abstract_methods(ByteString, '__getitem__', '__len__')
 
+    def test_Buffer(self):
+        for sample in [bytes, bytearray, memoryview]:
+            self.assertIsInstance(sample(b"x"), Buffer)
+            self.assertTrue(issubclass(sample, Buffer))
+        for sample in [str, list, tuple]:
+            self.assertNotIsInstance(sample(), Buffer)
+            self.assertFalse(issubclass(sample, Buffer))
+        self.validate_abstract_methods(Buffer, '__buffer__')
+
     def test_MutableSequence(self):
         for sample in [tuple, str, bytes]:
             self.assertNotIsInstance(sample(), MutableSequence)

Lib/test/test_doctest.py

@@ -707,7 +707,7 @@ def non_Python_modules(): r"""
 
     >>> import builtins
     >>> tests = doctest.DocTestFinder().find(builtins)
-    >>> 830 < len(tests) < 850 # approximate number of objects with docstrings
+    >>> 830 < len(tests) < 860 # approximate number of objects with docstrings
     True
     >>> real_tests = [t for t in tests if len(t.examples) > 0]
     >>> len(real_tests) # objects that actually have doctests

Misc/NEWS.d/next/Core and Builtins/2023-03-07-17-37-00.gh-issue-102500.RUSQhz.rst

@@ -0,0 +1,3 @@
+Make the buffer protocol accessible in Python code using the new
+``__buffer__`` and ``__release_buffer__`` magic methods. See :pep:`688` for
+details. Patch by Jelle Zijlstra.