improve documentation of DatasetFolder and ImageFolder (#2112) (#2409)

Summary: Pull Request resolved: #2409

Reviewed By: zhangguanheng66

Differential Revision: D22432518

Pulled By: fmassa

fbshipit-source-id: 7970c276b52315f7e5fa65a29d02407437af6d1a

torchvision/datasets/folder.py

@@ -80,7 +80,7 @@ class DatasetFolder(VisionDataset):
             both extensions and is_valid_file should not be passed.
 
      Attributes:
-        classes (list): List of the class names.
+        classes (list): List of the class names sorted alphabetically.
         class_to_idx (dict): Dict with items (class_name, class_index).
         samples (list): List of (sample path, class_index) tuples
         targets (list): The class_index value for each image in the dataset
@@ -198,7 +198,7 @@ class ImageFolder(DatasetFolder):
             and check if the file is a valid file (used to check of corrupt files)
 
      Attributes:
-        classes (list): List of the class names.
+        classes (list): List of the class names sorted alphabetically.
         class_to_idx (dict): Dict with items (class_name, class_index).
         imgs (list): List of (image path, class_index) tuples
     """