better testing for python 3+

skimage/measure/_marching_cubes_lewiner.py

@@ -3,7 +3,7 @@ import base64
 
 import numpy as np
 
-if sys.version_info[0] == 3:
+if sys.version_info >= (3, ):
     base64decode = base64.decodebytes
 else:
     base64decode = base64.decodestring

skimage/measure/mc_meta/createluts.py

@@ -13,8 +13,7 @@ import sys
 import base64
 
 # Get base64 encode/decode functions
-PY3 = sys.version_info[0] == 3
-if PY3:
+if sys.version_info >= (3, ):
     base64encode = base64.encodebytes
     base64decode = base64.decodebytes
 else:

skimage/measure/tests/test_marching_cubes.py

@@ -132,7 +132,7 @@ def test_both_algs_same_result_donut():
     n = 48
     a, b = 2.5/n, -1.25
     isovalue = 0.0
-    #
+    
     vol = np.empty((n,n,n), 'float32')
     for iz in range(vol.shape[0]):
         for iy in range(vol.shape[1]):