DEP: Deprecate use of axis=MAXDIMS instead of axis=None (#20920)

* added warning for axis=32

* corrected version to 1.23

* added tests for deprecation

* added newline EOF

* added newline EOF fix

* MAINT: Fixup deprecation text and add release note fragment

Co-authored-by: Sebastian Berg <sebastian@sipsolutions.net>

doc/release/upcoming_changes/20920.deprecation.rst

@@ -0,0 +1,3 @@
+* Using ``axis=32`` (``axis=np.MAXDIMS``) in many cases had the
+  same meaning as ``axis=None``.  This is deprecated and ``axis=None``
+  must be used instead.

numpy/core/src/multiarray/conversion_utils.c

@@ -332,6 +332,15 @@ PyArray_AxisConverter(PyObject *obj, int *axis)
         if (error_converting(*axis)) {
             return NPY_FAIL;
         }
+        if (*axis == NPY_MAXDIMS){
+            /* NumPy 1.23, 2022-05-19 */
+            if (DEPRECATE("Using `axis=32` (MAXDIMS) is deprecated. "
+                          "32/MAXDIMS had the same meaning as `axis=None` which "
+                          "should be used instead.  "
+                          "(Deprecated NumPy 1.23)") < 0) {
+                return NPY_FAIL;
+            }
+        }
     }
     return NPY_SUCCEED;
 }

numpy/core/tests/test_deprecations.py

@@ -1208,3 +1208,11 @@ class NoFinalize(np.ndarray):
             __array_finalize__ = None
 
         self.assert_deprecated(lambda: np.array(1).view(NoFinalize))
+
+class TestAxisNotMAXDIMS(_DeprecationTestCase):
+    # Deprecated 2022-01-08, NumPy 1.23
+    message = r"Using `axis=32` \(MAXDIMS\) is deprecated"
+
+    def test_deprecated(self):
+        a = np.zeros((1,)*32)
+        self.assert_deprecated(lambda: np.repeat(a, 1, axis=np.MAXDIMS))