NF+TST: add dtype attribute to Analyze arrayproxy

Add read-only dtype property to ArrayProxy class, and test with proxy
api tests, refactoring the dtype checking a bit on the way.

Author: matthew-brett

nibabel/arrayproxy.py

@@ -113,8 +113,12 @@ def shape(self):
         return self._shape
 
     @property
-    def is_proxy(self):
-        return True
+    def dtype(self):
+        return self._dtype
+
+    @property
+    def offset(self):
+        return self._offset
 
     @property
     def slope(self):
@@ -125,8 +129,8 @@ def inter(self):
         return self._inter
 
     @property
-    def offset(self):
-        return self._offset
+    def is_proxy(self):
+        return True
 
     def get_unscaled(self):
         ''' Read of data from file

nibabel/tests/test_proxy_api.py

@@ -59,7 +59,7 @@
 
 from numpy.testing import (assert_almost_equal, assert_array_equal)
 
-from ..testing import data_path as DATA_PATH
+from ..testing import data_path as DATA_PATH, assert_dt_equal
 
 from ..tmpdirs import InTemporaryDirectory
 
@@ -122,7 +122,7 @@ def validate_asarray(self, pmaker, params):
         prox, fio, hdr = pmaker()
         out = np.asarray(prox)
         assert_array_equal(out, params['arr_out'])
-        assert_equal(out.dtype.type, params['dtype_out'])
+        assert_dt_equal(out.dtype, params['dtype_out'])
         # Shape matches expected shape
         assert_equal(out.shape, params['shape'])
 
@@ -204,8 +204,8 @@ def obj_params(self):
                                                           slopes,
                                                           inters):
             n_els = np.prod(shape)
-            dt = np.dtype(dtype).newbyteorder(self.data_endian)
-            arr = np.arange(n_els, dtype=dt).reshape(shape)
+            dtype = np.dtype(dtype).newbyteorder(self.data_endian)
+            arr = np.arange(n_els, dtype=dtype).reshape(shape)
             data = arr.tostring(order=self.array_order)
             hdr = self.header_class()
             hdr.set_data_dtype(dtype)
@@ -264,6 +264,13 @@ def fname_func():
                 params = params.copy()
                 yield fname_func, params
 
+    def validate_dtype(self, pmaker, params):
+        # Read-only dtype attribute
+        prox, fio, hdr = pmaker()
+        assert_dt_equal(prox.dtype, params['dtype'])
+        assert_raises(AttributeError,
+                      prox.__setattr__, 'dtype', np.dtype(prox.dtype))
+
     def validate_slope_inter_offset(self, pmaker, params):
         # Check slope, inter, offset
         prox, fio, hdr = pmaker()