Merge pull request #799 from yarikoptic/enh-ignore-endianness

RF: compare data types using .dtype.type to avoid effect of endianness

Author: effigies

nibabel/cmdline/diff.py

@@ -9,6 +9,11 @@
 ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ##
 """
 Quick summary of the differences among a set of neuroimaging files
+
+Notes:
+    - difference in data types for header fields will be detected, but
+      endianness difference will not be detected. It is done so to compare files
+      with native endianness used in data files.
 """
 from __future__ import division, print_function, absolute_import
 
@@ -99,7 +104,8 @@ def are_values_different(*values):
         if type(value0) != type(value):  # if types are different, then we consider them different
             return True
         elif isinstance(value0, np.ndarray):
-            if value0.dtype != value.dtype or \
+            # use .dtype.type to provide endianness agnostic comparison
+            if value0.dtype.type != value.dtype.type or \
                value0.shape != value.shape:
                 return True
             # there might be nans and they need special treatment

nibabel/tests/test_diff.py

@@ -72,3 +72,9 @@ def test_diff_values_array():
     # and some inf should not be a problem
     assert not are_values_different(array([0, inf]), array([0, inf]))
     assert are_values_different(array([0, inf]), array([inf, 0]))
+
+    # we will allow for types to be of different endianness but the
+    # same in "instnatiation" type and value
+    assert not are_values_different(np.array(1, dtype='<i4'), np.array(1, dtype='>i4'))
+    # but do report difference if instantiation type is different:
+    assert are_values_different(np.array(1, dtype='<i4'), np.array(1, dtype='<i2'))