Added PyDataType_SHAPE

Cython/Includes/numpy.pxd

@@ -176,7 +176,8 @@ cdef extern from "numpy/arrayobject.h":
         cdef object fields
         cdef tuple names
         # Use PyDataType_HASSUBARRAY to test whether this field is
-        # valid (the pointer can be NULL).
+        # valid (the pointer can be NULL). Most users should access
+        # this field via the inline helper method PyDataType_SHAPE.
         cdef PyArray_ArrayDescr* subarray
 
     ctypedef extern class numpy.flatiter [object PyArrayIterObject]:
@@ -798,6 +799,12 @@ cdef inline object PyArray_MultiIterNew4(a, b, c, d):
 cdef inline object PyArray_MultiIterNew5(a, b, c, d, e):
     return PyArray_MultiIterNew(5, <void*>a, <void*>b, <void*>c, <void*> d, <void*> e)
 
+cdef inline tuple PyDataType_SHAPE(dtype d):
+    if PyDataType_HASSUBARRAY(d):
+        return <tuple>d.subarray.shape
+    else:
+        return None
+
 cdef inline char* _util_dtypestring(dtype descr, char* f, char* end, int* offset) except NULL:
     # Recursive utility function used in __getbuffer__ to get format
     # string. The new location in the format string is returned.

tests/run/numpy_subarray.pyx

@@ -19,10 +19,19 @@ def test_record_subarray():
     cdef np.dtype a_descr = descr.fields['a'][0]
     cdef np.dtype b_descr = descr.fields['b'][0]
 
+    # Make sure the dtype looks like we expect
     assert descr.fields == {'a': (py_numpy.dtype('int32'), 0),
                             'b': (py_numpy.dtype(('<f8', (3, 3))), 4)}
+
+    # Make sure that HASSUBARRAY is working
     assert not np.PyDataType_HASSUBARRAY(descr)
     assert not np.PyDataType_HASSUBARRAY(a_descr)
     assert np.PyDataType_HASSUBARRAY(b_descr)
 
+    # Make sure the direct field access works
     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(b_descr) == (3, 3)