tweak to PyDataType_SHAPE: return () instead of None

This makes PyDataType_SHAPE more consistent with the Python API.

Cython/Includes/numpy.pxd

@@ -803,7 +803,7 @@ cdef inline tuple PyDataType_SHAPE(dtype d):
     if PyDataType_HASSUBARRAY(d):
         return <tuple>d.subarray.shape
     else:
-        return None
+        return ()
 
 cdef inline char* _util_dtypestring(dtype descr, char* f, char* end, int* offset) except NULL:
     # Recursive utility function used in __getbuffer__ to get format

tests/run/numpy_subarray.pyx

@@ -32,6 +32,6 @@ def test_record_subarray():
     assert <tuple>b_descr.subarray.shape == (3, 3)
 
     # Make sure the safe high-level helper function works
-    assert np.PyDataType_SHAPE(descr) is None
-    assert np.PyDataType_SHAPE(a_descr) is None
+    assert np.PyDataType_SHAPE(descr) == ()
+    assert np.PyDataType_SHAPE(a_descr) == ()
     assert np.PyDataType_SHAPE(b_descr) == (3, 3)