BUG: regression for array([pandas.DataFrame()]) (#13663)

Fixup of gh-13399 to avoid a regression with pandas. The actual output after this is the same as
before, but incorrect with respect to the output shape. However, it seems a bit larger and an issue
to look at after the 1.17 release.

* BUG: test, fix regression for array([pandas.DataFrame()])

* BUG: refactor to make sure tmp is DECREFfed

2 files changed, 44 insertions, 20 deletions

diff --git a/numpy/core/src/multiarray/ctors.c b/numpy/core/src/multiarray/ctors.c
index 8e09de1c8..4b524c365 100644
--- a/numpy/core/src/multiarray/ctors.c
+++ b/numpy/core/src/multiarray/ctors.c
@@ -439,7 +439,6 @@ static int
 setArrayFromSequence(PyArrayObject *a, PyObject *s,
                         int dim, PyArrayObject * dst)
 {
-    PyObject *tmp;
     Py_ssize_t i, slen;
     int res = -1;
 
@@ -447,11 +446,6 @@ setArrayFromSequence(PyArrayObject *a, PyObject *s,
     if (dst == NULL)
         dst = a;
 
-    /*
-     * This code is to ensure that the sequence access below will
-     * return a lower-dimensional sequence.
-     */
-
     /* INCREF on entry DECREF on exit */
     Py_INCREF(s);
 
@@ -477,32 +471,42 @@ setArrayFromSequence(PyArrayObject *a, PyObject *s,
         return 0;
     }
 
+    /*
+     * This code is to ensure that the sequence access below will
+     * return a lower-dimensional sequence.
+     */
+
     if (dim > PyArray_NDIM(a)) {
         PyErr_Format(PyExc_ValueError,
                  "setArrayFromSequence: sequence/array dimensions mismatch.");
         goto fail;
     }
 
-    tmp = _array_from_array_like(s, /*dtype*/NULL, /*writeable*/0, /*context*/NULL);
-    if (tmp == NULL) {
+    slen = PySequence_Length(s);
+    if (slen < 0) {
         goto fail;
     }
-    else if (tmp != Py_NotImplemented) {
-        if (PyArray_CopyInto(dst, (PyArrayObject *)tmp) < 0) {
+    if (slen > 0) {
+        /* gh-13659: try __array__ before using s as a sequence */
+        PyObject *tmp = _array_from_array_like(s, /*dtype*/NULL, /*writeable*/0,
+                                               /*context*/NULL);
+        if (tmp == NULL) {
             goto fail;
         }
-
-        Py_DECREF(s);
-        return 0;
-    }
-    else {
-        Py_DECREF(Py_NotImplemented);
+        else if (tmp == Py_NotImplemented) {
+            Py_DECREF(tmp);
+        }
+        else {
+            int r = PyArray_CopyInto(dst, (PyArrayObject *)tmp);
+            Py_DECREF(tmp);
+            if (r < 0) {
+                goto fail;
+            }
+            Py_DECREF(s);
+            return 0;
+        }
     }
 
-    slen = PySequence_Length(s);
-    if (slen < 0) {
-        goto fail;
-    }
     /*
      * Either the dimensions match, or the sequence has length 1 and can
      * be broadcast to the destination.
diff --git a/numpy/core/tests/test_regression.py b/numpy/core/tests/test_regression.py
index 4e48c82b7..e564ae300 100644
--- a/numpy/core/tests/test_regression.py
+++ b/numpy/core/tests/test_regression.py
@@ -2454,3 +2454,23 @@ class TestRegression(object):
             __array_interface__ = {}
 
         np.array([T()])
+
+    def test_2d__array__shape(self):
+        class T(object):
+            def __array__(self):
+                return np.ndarray(shape=(0,0))
+
+            # Make sure __array__ is used instead of Sequence methods.
+            def __iter__(self):
+                return iter([])
+
+            def __getitem__(self, idx):
+                raise AssertionError("__getitem__ was called")
+
+            def __len__(self):
+                return 0
+
+
+        t = T()
+        #gh-13659, would raise in broadcasting [x=t for x in result]
+        np.array([t])