Sync selectors.py with upstream asyncio

Lib/selectors.py

@@ -49,11 +49,12 @@ SelectorKey.__doc__ = """SelectorKey(fileobj, fd, events, data)
     Object used to associate a file object to its backing
     file descriptor, selected event mask, and attached data.
 """
-SelectorKey.fileobj.__doc__ = 'File object registered.'
-SelectorKey.fd.__doc__ = 'Underlying file descriptor.'
-SelectorKey.events.__doc__ = 'Events that must be waited for on this file object.'
-SelectorKey.data.__doc__ = ('''Optional opaque data associated to this file object.
-For example, this could be used to store a per-client session ID.''')
+if sys.version_info >= (3, 5):
+    SelectorKey.fileobj.__doc__ = 'File object registered.'
+    SelectorKey.fd.__doc__ = 'Underlying file descriptor.'
+    SelectorKey.events.__doc__ = 'Events that must be waited for on this file object.'
+    SelectorKey.data.__doc__ = ('''Optional opaque data associated to this file object.
+    For example, this could be used to store a per-client session ID.''')
 
 class _SelectorMapping(Mapping):
     """Mapping of file objects to selector keys."""