Merge pull request #636 from ANTsX/test-write-transform

ENH: check for transform instance before writing to file

ants/core/ants_transform_io.py

@@ -375,6 +375,9 @@ def write_transform(transform, filename):
     >>> ants.write_transform(tx, '~/desktop/tx.mat')
     >>> tx2 = ants.read_transform('~/desktop/tx.mat')
     """
+    if not isinstance(transform, tio.ANTsTransform):
+        raise Exception('Only ANTsTransform instances can be written to file. Check that you are not passing in a filepath to a saved transform.')
+
     filename = os.path.expanduser(filename)
     libfn = utils.get_lib_fn("writeTransform")
     libfn(transform.pointer, filename)

tests/test_core_ants_transform_io.py

@@ -113,7 +113,11 @@ def test_to_displacement(self):
         mytx = ants.registration(fixed=fi, moving=mi, type_of_transform = ('SyN') )
         vec = ants.image_read( mytx['fwdtransforms'][0] )
         atx = ants.transform_from_displacement_field( vec )
-        field = ants.transform_to_displacement_field( atx, fi )    
+        field = ants.transform_to_displacement_field( atx, fi )   
+
+    def test_catch_error(self):
+        with self.assertRaises(Exception):
+            ants.write_transform(123, 'test.mat') 
 
 
 if __name__ == '__main__':