Fix im_class access in Python 3.

skimage/_shared/utils.py

@@ -1,5 +1,6 @@
 import warnings
 import functools
+import sys
 
 from . import six
 
@@ -54,3 +55,10 @@ class deprecated(object):
             wrapped.__doc__ = doc + '\n\n    ' + wrapped.__doc__
 
         return wrapped
+
+
+def get_bound_method_class(m):
+    """Return the class for a bound method.
+
+    """
+    return m.im_class if sys.version < '3' else m.__self__.__class__

skimage/transform/_geometric.py

@@ -4,6 +4,7 @@ from scipy import ndimage, spatial
 from skimage.util import img_as_float
 from ._warps_cy import _warp_fast
 
+from skimage._shared.utils import get_bound_method_class
 
 class GeometricTransform(object):
     """Perform geometric transformations on a set of coordinates.
@@ -1009,8 +1010,8 @@ def warp(image, inverse_map=None, map_args={}, output_shape=None, order=1,
         if inverse_map in HOMOGRAPHY_TRANSFORMS:
             matrix = inverse_map._matrix
         elif hasattr(inverse_map, '__name__') \
-                and inverse_map.__name__ == 'inverse' \
-                and inverse_map.im_class in HOMOGRAPHY_TRANSFORMS:
+             and inverse_map.__name__ == 'inverse' \
+             and get_bound_method_class(inverse_map) in HOMOGRAPHY_TRANSFORMS:
             matrix = np.linalg.inv(inverse_map.im_self._matrix)
         if matrix is not None:
             # transform all bands