RF: Remove endianness, override copy, as_byteswapped, diagnose_binaryblock

Author: effigies

nibabel/freesurfer/mghformat.py

@@ -92,7 +92,6 @@ class MGHHeader(LabeledWrapStruct):
 
     def __init__(self,
                  binaryblock=None,
-                 endianness='>',
                  check=True):
         ''' Initialize header from binary data block
 
@@ -105,9 +104,6 @@ def __init__(self,
             Whether to check content of header in initialization.
             Default is True.
         '''
-        if endianness != '>':
-            raise ValueError("MGHHeader is big-endian")
-
         min_size = self._hdrdtype.itemsize
         full_size = self.template_dtype.itemsize
         if binaryblock is not None and len(binaryblock) >= min_size:
@@ -117,7 +113,7 @@ def __init__(self,
             binaryblock = (binaryblock[:full_size] +
                            b'\x00' * (full_size - len(binaryblock)))
         super(MGHHeader, self).__init__(binaryblock=binaryblock,
-                                        endianness=endianness,
+                                        endianness='big',
                                         check=False)
         if not self._structarr['goodRASFlag']:
             self._set_affine_default()
@@ -408,6 +404,42 @@ def writeftr_to(self, fileobj):
         fileobj.seek(self.get_footer_offset())
         fileobj.write(ftr_nd.tostring())
 
+    def copy(self):
+        ''' Return copy of structure '''
+        return self.__class__(self.binaryblock, check=False)
+
+    def as_byteswapped(self, endianness=None):
+        ''' Return new object with given ``endianness``
+
+        If big endian, returns a copy of the object. Otherwise raises ValueError.
+
+        Parameters
+        ----------
+        endianness : None or string, optional
+           endian code to which to swap.  None means swap from current
+           endianness, and is the default
+
+        Returns
+        -------
+        wstr : ``MGHHeader``
+           ``MGHHeader`` object
+
+        '''
+        if endianness is None or endian_codes[endianness] != '>':
+            raise ValueError('Cannot byteswap MGHHeader - '
+                             'must always be big endian')
+        return self.copy()
+
+    @classmethod
+    def diagnose_binaryblock(klass, binaryblock, endianness=None):
+        if endianness is not None and endian_codes[endianness] != '>':
+            raise ValueError('MGHHeader must always be big endian')
+        wstr = klass(binaryblock, check=False)
+        battrun = BatteryRunner(klass._get_checks())
+        reports = battrun.check_only(wstr)
+        return '\n'.join([report.message
+                          for report in reports if report.message])
+
     class _HeaderData:
         """ Provide interface to deprecated MGHHeader fields"""
         def __init__(self, structarr):

nibabel/freesurfer/tests/test_mghformat.py

@@ -41,6 +41,17 @@
                    [0.0, -1.0, 0.0, 2.0],
                    [0.0, 0.0, 0.0, 1.0]], dtype=np.float32)
 
+BIG_CODES = ('>', 'big', 'BIG', 'b', 'be', 'B', 'BE')
+LITTLE_CODES = ('<', 'little', 'l', 'le', 'L', 'LE')
+
+if sys_is_le:
+    BIG_CODES += ('swapped', 's', 'S', '!')
+    LITTLE_CODES += ('native', 'n', 'N', '=', '|', 'i', 'I')
+else:
+    BIG_CODES += ('native', 'n', 'N', '=', '|', 'i', 'I')
+    LITTLE_CODES += ('swapped', 's', 'S', '!')
+
+
 
 def test_read_mgh():
     # test.mgz was generated by the following command
@@ -258,12 +269,6 @@ def test_mgh_load_fileobj():
     assert_array_equal(img.get_data(), img2.get_data())
 
 
-def test_mgh_reject_little_endian():
-    bblock = b'\x00' * MGHHeader.template_dtype.itemsize
-    with assert_raises(ValueError):
-        MGHHeader(bblock, endianness='<')
-
-
 def test_mgh_affine_default():
     hdr = MGHHeader()
     hdr['goodRASFlag'] = 0
@@ -303,26 +308,29 @@ def test_mghheader_default_structarr():
     assert_equal(hdr['ti'], 0)
     assert_equal(hdr['fov'], 0)
 
-    big_codes = ('>', 'big', 'BIG', 'b', 'be', 'B', 'BE')
-    little_codes = ('<', 'little', 'l', 'le', 'L', 'LE')
-
-    if sys_is_le:
-        big_codes += ('swapped', 's', 'S', '!')
-        little_codes += ('native', 'n', 'N', '=', '|', 'i', 'I')
-    else:
-        big_codes += ('native', 'n', 'N', '=', '|', 'i', 'I')
-        little_codes += ('swapped', 's', 'S', '!')
-
-    for endianness in big_codes:
+    for endianness in (None,) + BIG_CODES:
         hdr2 = MGHHeader.default_structarr(endianness=endianness)
         assert_equal(hdr2, hdr)
         assert_equal(hdr2.newbyteorder('>'), hdr)
 
-    for endianness in little_codes:
+    for endianness in LITTLE_CODES:
         with assert_raises(ValueError):
             MGHHeader.default_structarr(endianness=endianness)
 
 
+def test_byteswap():
+    hdr = MGHHeader()
+
+    for endianness in BIG_CODES:
+        hdr2 = hdr.as_byteswapped(endianness)
+        assert_true(hdr2 is not hdr)
+        assert_equal(hdr2, hdr)
+
+    for endianness in (None,) + LITTLE_CODES:
+        with assert_raises(ValueError):
+            hdr.as_byteswapped(endianness)
+
+
 class TestMGHImage(tsi.TestSpatialImage, tsi.MmapImageMixin):
     """ Apply general image tests to MGHImage
     """