bpo-33176: Add a toreadonly() method to memoryviews. (GH-6466)

2 files changed, 34 insertions, 16 deletions

diff --git a/Lib/test/test_buffer.py b/Lib/test/test_buffer.py
index f302da4..a3f3ef0 100644
--- a/Lib/test/test_buffer.py
+++ b/Lib/test/test_buffer.py
@@ -924,23 +924,30 @@ class TestBufferProtocol(unittest.TestCase):
             except BufferError: # re-exporter does not provide full information
                 return
             ex = result.obj if isinstance(result, memoryview) else result
-            self.assertIs(m.obj, ex)
-            self.assertEqual(m.nbytes, expected_len)
-            self.assertEqual(m.itemsize, itemsize)
-            self.assertEqual(m.format, fmt)
-            self.assertEqual(m.readonly, readonly)
-            self.assertEqual(m.ndim, ndim)
-            self.assertEqual(m.shape, tuple(shape))
-            if not (sliced and suboffsets):
-                self.assertEqual(m.strides, tuple(strides))
-            self.assertEqual(m.suboffsets, tuple(suboffsets))
-
-            n = 1 if ndim == 0 else len(lst)
-            self.assertEqual(len(m), n)
 
-            rep = result.tolist() if fmt else result.tobytes()
-            self.assertEqual(rep, lst)
-            self.assertEqual(m, result)
+            def check_memoryview(m, expected_readonly=readonly):
+                self.assertIs(m.obj, ex)
+                self.assertEqual(m.nbytes, expected_len)
+                self.assertEqual(m.itemsize, itemsize)
+                self.assertEqual(m.format, fmt)
+                self.assertEqual(m.readonly, expected_readonly)
+                self.assertEqual(m.ndim, ndim)
+                self.assertEqual(m.shape, tuple(shape))
+                if not (sliced and suboffsets):
+                    self.assertEqual(m.strides, tuple(strides))
+                self.assertEqual(m.suboffsets, tuple(suboffsets))
+
+                n = 1 if ndim == 0 else len(lst)
+                self.assertEqual(len(m), n)
+
+                rep = result.tolist() if fmt else result.tobytes()
+                self.assertEqual(rep, lst)
+                self.assertEqual(m, result)
+
+            check_memoryview(m)
+            with m.toreadonly() as mm:
+                check_memoryview(mm, expected_readonly=True)
+            m.tobytes()  # Releasing mm didn't release m
 
     def verify_getbuf(self, orig_ex, ex, req, sliced=False):
         def simple_fmt(ex):
diff --git a/Lib/test/test_memoryview.py b/Lib/test/test_memoryview.py
index ddd5b9a..ca307d8 100644
--- a/Lib/test/test_memoryview.py
+++ b/Lib/test/test_memoryview.py
@@ -362,6 +362,17 @@ class AbstractMemoryTests:
             self.assertEqual(list(reversed(m)), aslist)
             self.assertEqual(list(reversed(m)), list(m[::-1]))
 
+    def test_toreadonly(self):
+        for tp in self._types:
+            b = tp(self._source)
+            m = self._view(b)
+            mm = m.toreadonly()
+            self.assertTrue(mm.readonly)
+            self.assertTrue(memoryview(mm).readonly)
+            self.assertEqual(mm.tolist(), m.tolist())
+            mm.release()
+            m.tolist()
+
     def test_issue22668(self):
         a = array.array('H', [256, 256, 256, 256])
         x = memoryview(a)