BF - allow for None affine in SPM images

None affine results in no write to the mat file object, and reading from
an empty mat file object raised an error.  Test and fix.

Author: matthew-brett

nibabel/spm99analyze.py

@@ -10,6 +10,8 @@
 import warnings
 import numpy as np
 
+from .py3k import BytesIO
+
 from .spatialimages import HeaderDataError, HeaderTypeError
 
 from .batteryrunners import Report
@@ -246,14 +248,18 @@ class Spm99AnalyzeImage(analyze.AnalyzeImage):
     @classmethod
     def from_file_map(klass, file_map):
         ret = super(Spm99AnalyzeImage, klass).from_file_map(file_map)
-        import scipy.io as sio
         try:
             matf = file_map['mat'].get_prepare_fileobj()
         except IOError:
             return ret
-        mats = sio.loadmat(matf)
+        # Allow for possibility of empty file -> no update to affine
+        contents = matf.read()
         if file_map['mat'].filename is not None: # was filename
             matf.close()
+        if len(contents) == 0:
+            return ret
+        import scipy.io as sio
+        mats = sio.loadmat(BytesIO(contents))
         if 'mat' in mats: # this overrides a 'M', and includes any flip
             mat = mats['mat']
             if mat.ndim > 2:

nibabel/tests/test_spm99analyze.py

@@ -157,6 +157,20 @@ def test_mat_read(self):
         assert_array_equal(r_img.get_affine(),
                            np.dot(np.diag([3,4,5,1]), np.dot(flipper, to_111)))
 
+    def test_none_affine(self):
+        # Allow for possibility of no affine resulting in nothing written into
+        # mat file.  If the mat file is a filename, we just get no file, but if
+        # it's a fileobj, we get an empty fileobj
+        img_klass = self.image_class
+        # With a None affine - no matfile written
+        img = img_klass(np.zeros((2,3,4)), None)
+        aff = img.get_header().get_best_affine()
+        # Save / reload using bytes IO objects
+        for key, value in img.file_map.items():
+            value.fileobj = BytesIO()
+        img.to_file_map()
+        img_back = img.from_file_map(img.file_map)
+        assert_array_equal(img_back.get_affine(), aff)
 
 
 def test_origin_affine():