fix add_start_docstrings on python 2 (removed)

pytorch_transformers/modeling_utils.py

@@ -15,17 +15,20 @@
 # limitations under the License.
 """PyTorch BERT model."""
 
-from __future__ import absolute_import, division, print_function, unicode_literals
+from __future__ import (absolute_import, division, print_function,
+                        unicode_literals)
 
+import copy
+import json
 import logging
 import os
-import json
-import copy
 from io import open
 
+import six
 import torch
 from torch import nn
-from torch.nn import CrossEntropyLoss, functional as F
+from torch.nn import CrossEntropyLoss
+from torch.nn import functional as F
 
 from .file_utils import cached_path
 
@@ -36,11 +39,18 @@ WEIGHTS_NAME = "pytorch_model.bin"
 TF_WEIGHTS_NAME = 'model.ckpt'
 
 
-def add_start_docstrings(*docstr):
-    def docstring_decorator(fn):
-        fn.__doc__ = ''.join(docstr) + fn.__doc__
-        return fn
-    return docstring_decorator
+if not six.PY2:
+    def add_start_docstrings(*docstr):
+        def docstring_decorator(fn):
+            fn.__doc__ = ''.join(docstr) + fn.__doc__
+            return fn
+        return docstring_decorator
+else:
+    # Not possible to update class docstrings on python2
+    def add_start_docstrings(*docstr):
+        def docstring_decorator(fn):
+            return fn
+        return docstring_decorator
 
 
 class PretrainedConfig(object):