gh-102500: Implement PEP 688 (#102521)

Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>

Lib/test/test_buffer.py

@@ -17,6 +17,7 @@ import contextlib
 import unittest
 from test import support
 from test.support import os_helper
+import inspect
 from itertools import permutations, product
 from random import randrange, sample, choice
 import warnings
@@ -4438,5 +4439,146 @@ class TestBufferProtocol(unittest.TestCase):
                              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 NoBytesEither:
+            def __buffer__(self, flags):
+                return b"hello"
+
+        self.assertRaises(TypeError, memoryview, NoBytesEither())
+
+        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_buffer_flags(self):
+        class PossiblyMutable:
+            def __init__(self, data, mutable) -> None:
+                self._data = bytearray(data)
+                self._mutable = mutable
+
+            def __buffer__(self, flags):
+                if flags & inspect.BufferFlags.WRITABLE:
+                    if not self._mutable:
+                        raise RuntimeError("not mutable")
+                    return memoryview(self._data)
+                else:
+                    return memoryview(bytes(self._data))
+
+        mutable = PossiblyMutable(b"hello", True)
+        immutable = PossiblyMutable(b"hello", False)
+        with memoryview._from_flags(mutable, inspect.BufferFlags.WRITABLE) as mv:
+            self.assertEqual(mv.tobytes(), b"hello")
+            mv[0] = ord(b'x')
+            self.assertEqual(mv.tobytes(), b"xello")
+        with memoryview._from_flags(mutable, inspect.BufferFlags.SIMPLE) as mv:
+            self.assertEqual(mv.tobytes(), b"xello")
+            with self.assertRaises(TypeError):
+                mv[0] = ord(b'h')
+            self.assertEqual(mv.tobytes(), b"xello")
+        with memoryview._from_flags(immutable, inspect.BufferFlags.SIMPLE) as mv:
+            self.assertEqual(mv.tobytes(), b"hello")
+            with self.assertRaises(TypeError):
+                mv[0] = ord(b'x')
+            self.assertEqual(mv.tobytes(), b"hello")
+
+        with self.assertRaises(RuntimeError):
+            memoryview._from_flags(immutable, inspect.BufferFlags.WRITABLE)
+        with memoryview(immutable) as mv:
+            self.assertEqual(mv.tobytes(), b"hello")
+            with self.assertRaises(TypeError):
+                mv[0] = ord(b'x')
+            self.assertEqual(mv.tobytes(), b"hello")
+
+    def test_call_builtins(self):
+        ba = bytearray(b"hello")
+        mv = ba.__buffer__(0)
+        self.assertEqual(mv.tobytes(), b"hello")
+        ba.__release_buffer__(mv)
+        with self.assertRaises(OverflowError):
+            ba.__buffer__(sys.maxsize + 1)
+
+    @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()