gh-125420: implement Sequence.__contains__ API on memoryview objects

Lib/test/test_memoryview.py

@@ -90,6 +90,24 @@ def test_iter(self):
             m = self._view(b)
             self.assertEqual(list(m), [m[i] for i in range(len(m))])
 
+    def test_contains(self):
+        for tp in self._types:
+            b = tp(self._source)
+            m = self._view(b)
+            for c in list(m):
+                with self.subTest(self._source, buffer_type=tp, item=c):
+                    self.assertIn(c, m)
+
+            with self.subTest('empty buffer'):
+                empty = tp(b'')
+                mview = self._view(empty)
+                self.assertNotIn(0, mview)
+
+            with self.subTest('not found'):
+                b = tp(b'abc')
+                m = self._view(b)
+                self.assertNotIn(ord('d'), m)
+
     def test_count(self):
         for tp in self._types:
             b = tp(self._source)

Misc/NEWS.d/next/Core_and_Builtins/2024-10-14-12-17-00.gh-issue-125420.hpMz9A.rst

@@ -0,0 +1,2 @@
+Implement :meth:`~object.__contains__` for :class:`memoryview` objects.
+Patch by Bénédikt Tran.

Objects/memoryobject.c

@@ -2483,6 +2483,37 @@ memory_item_multi(PyMemoryViewObject *self, PyObject *tup)
     return unpack_single(self, ptr, fmt);
 }
 
+/* Test the membership of an item. */
+static int
+memory_contains(PyObject *self, PyObject *value)
+{
+    PyObject *iter = PyObject_GetIter(self);
+    if (iter == NULL) {
+        return -1;
+    }
+
+    PyObject *item = NULL;
+    while (PyIter_NextItem(iter, &item)) {
+        if (item == NULL) {
+            Py_DECREF(iter);
+            return -1;
+        }
+        if (item == value) {
+            Py_DECREF(item);
+            Py_DECREF(iter);
+            return 1;
+        }
+        int contained = PyObject_RichCompareBool(item, value, Py_EQ);
+        Py_DECREF(item);
+        if (contained != 0) {
+            Py_DECREF(iter);
+            return contained;
+        }
+    }
+    Py_DECREF(iter);
+    return 0;
+}
+
 static inline int
 init_slice(Py_buffer *base, PyObject *key, int dim)
 {
@@ -2741,10 +2772,9 @@ static PyMappingMethods memory_as_mapping = {
 
 /* As sequence */
 static PySequenceMethods memory_as_sequence = {
-        memory_length,                    /* sq_length */
-        0,                                /* sq_concat */
-        0,                                /* sq_repeat */
-        memory_item,                      /* sq_item */
+    .sq_length = memory_length,
+    .sq_item = memory_item,
+    .sq_contains = memory_contains
 };