Merge pull request #21728 from charris/backport-21632maintenance/1.22.x

API: Retain `arr.base` more strictly in `np.frombuffer`

2 files changed, 16 insertions, 14 deletions

diff --git a/numpy/core/src/multiarray/ctors.c b/numpy/core/src/multiarray/ctors.c
index c5a7ebf7d..bbd73e280 100644
--- a/numpy/core/src/multiarray/ctors.c
+++ b/numpy/core/src/multiarray/ctors.c
@@ -3685,15 +3685,16 @@ PyArray_FromBuffer(PyObject *buf, PyArray_Descr *type,
     }
 
     /*
-     * The array check is probably unnecessary.  It preserves the base for
-     * arrays.  This is the "old" buffer protocol, which had no release logic.
-     * (It was assumed that the result is always a view.)
-     *
-     * NOTE: We could also check if `bf_releasebuffer` is defined which should
-     *       be the most precise and safe thing to do.  But that should only be
-     *       necessary if unexpected backcompat issues are found downstream.
+     * If the object supports `releasebuffer`, the new buffer protocol allows
+     * tying the memories lifetime to the `Py_buffer view`.
+     * NumPy cannot hold on to the view itself (it is not an object) so it
+     * has to wrap the original object in a Python `memoryview` which deals
+     * with the lifetime management for us.
+     * For backwards compatibility of `arr.base` we try to avoid this when
+     * possible.  (For example, NumPy arrays will never get wrapped here!)
      */
-    if (!PyArray_Check(buf)) {
+    if (Py_TYPE(buf)->tp_as_buffer
+            && Py_TYPE(buf)->tp_as_buffer->bf_releasebuffer) {
         buf = PyMemoryView_FromObject(buf);
         if (buf == NULL) {
             return NULL;
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index 35acf307f..deb706752 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -5350,12 +5350,13 @@ class TestFromBuffer:
         buf = x.tobytes()
         assert_array_equal(np.frombuffer(buf, dtype=dt), x.flat)
 
-    def test_array_base(self):
-        arr = np.arange(10)
-        new = np.frombuffer(arr)
-        # We currently special case arrays to ensure they are used as a base.
-        # This could probably be changed (removing the test).
-        assert new.base is arr
+    @pytest.mark.parametrize("obj", [np.arange(10), b"12345678"])
+    def test_array_base(self, obj):
+        # Objects (including NumPy arrays), which do not use the
+        # `release_buffer` slot should be directly used as a base object.
+        # See also gh-21612
+        new = np.frombuffer(obj)
+        assert new.base is obj
 
     def test_empty(self):
         assert_array_equal(np.frombuffer(b''), np.array([]))