Relegate slicing to is_header, remove _minctest

Use more definitive test for MINC1 images
Remove unused import

Author: effigies

nibabel/minc1.py

@@ -14,7 +14,6 @@
 
 from .externals.netcdf import netcdf_file
 
-from .filename_parser import splitext_addext
 from .spatialimages import Header, SpatialImage
 from .fileslice import canonical_slicers
 
@@ -284,7 +283,7 @@ def data_from_fileobj(self, fileobj):
 class Minc1Header(MincHeader):
     @classmethod
     def is_header(klass, binaryblock):
-        return binaryblock != b'\211HDF'
+        return binaryblock[:4] == 'CDF\x01'
 
 
 class Minc1Image(SpatialImage):

nibabel/minc2.py

@@ -137,7 +137,7 @@ def get_scaled_data(self, sliceobj=()):
 class Minc2Header(MincHeader):
     @classmethod
     def is_header(klass, binaryblock):
-        return binaryblock == b'\211HDF'
+        return binaryblock[:4] == b'\211HDF'
 
 
 class Minc2Image(Minc1Image):
@@ -167,9 +167,5 @@ def from_file_map(klass, file_map):
         data = klass.ImageArrayProxy(minc_file)
         return klass(data, affine, header, extra=None, file_map=file_map)
 
-    @classmethod
-    def _minctest(klass, binaryblock):
-        return binaryblock[:4] == b'\211HDF'
-
 
 load = Minc2Image.load

nibabel/spatialimages.py

@@ -912,7 +912,7 @@ def is_image(klass, filename, sniff=None):
                 with ImageOpener(metadata_filename, 'rb') as fobj:
                     sniff = fobj.read(sizeof_hdr)
 
-            is_header = klass.header_class.is_header(sniff[:klass_sizeof_hdr])
+            is_header = klass.header_class.is_header(sniff)
         except Exception as e:
             # Can happen if: file doesn't exist,
             #   filesize < necessary sniff size (this happens!)