Correctly check for string type.

skimage/io/_io.py

@@ -15,6 +15,7 @@ import numpy as np
 
 from skimage.io._plugins import call as call_plugin
 from skimage.color import rgb2grey
+from skimage._shared import six
 
 
 # Shared image queue
@@ -25,7 +26,7 @@ URL_REGEX = re.compile(r'http://|https://|ftp://|file://|file:\\')
 
 def is_url(filename):
     """Return True if string is an http or ftp path."""
-    return (isinstance(filename, basestring) and
+    return (isinstance(filename, six.string_types) and
             URL_REGEX.match(filename) is not None)
 
 
@@ -220,7 +221,7 @@ def imshow(arr, plugin=None, **plugin_args):
         Passed to the given plugin.
 
     """
-    if isinstance(arr, basestring):
+    if isinstance(arr, six.string_types):
         arr = call_plugin('imread', arr, plugin=plugin)
     return call_plugin('imshow', arr, plugin=plugin, **plugin_args)
 

skimage/io/collection.py

@@ -10,6 +10,7 @@ from copy import copy
 
 import numpy as np
 from ._io import imread
+from .._shared import six
 
 
 def concatenate_images(ic):
@@ -296,7 +297,7 @@ class ImageCollection(object):
     """
     def __init__(self, load_pattern, conserve_memory=True, load_func=None):
         """Load and manage a collection of images."""
-        if isinstance(load_pattern, basestring):
+        if isinstance(load_pattern, six.string_types):
             load_pattern = load_pattern.split(':')
             self._files = []
             for pattern in load_pattern:

skimage/io/tests/test_collection.py

@@ -12,6 +12,7 @@ from skimage import data_dir
 from skimage.io import ImageCollection, MultiImage
 from skimage.io.collection import alphanumeric_key
 from skimage.io import Image as ioImage
+from skimage._shared import six
 
 
 try:
@@ -21,8 +22,6 @@ except ImportError:
 else:
     PIL_available = True
 
-if sys.version_info[0] > 2:
-    basestring = str
 
 class TestAlphanumericKey():
     def setUp(self):
@@ -129,7 +128,7 @@ class TestMultiImage():
 
     @skipif(not PIL_available)
     def test_files_property(self):
-        assert isinstance(self.img.filename, basestring)
+        assert isinstance(self.img.filename, six.string_types)
 
         def set_filename(f):
             self.img.filename = f

skimage/viewer/plugins/overlayplugin.py

@@ -3,6 +3,7 @@ from warnings import warn
 from skimage.util.dtype import dtype_range
 from .base import Plugin
 from ..utils import ClearColormap, update_axes_image
+from skimage._shared import six
 
 
 __all__ = ['OverlayPlugin']
@@ -77,7 +78,8 @@ class OverlayPlugin(Plugin):
     @color.setter
     def color(self, index):
         # Update colormap whenever color is changed.
-        if isinstance(index, basestring) and index not in self.color_names:
+        if isinstance(index, six.string_types) and \
+           index not in self.color_names:
             raise ValueError("%s not defined in OverlayPlugin.colors" % index)
         else:
             name = self.color_names[index]