Support Arrow reader not requiring closing

fixlength_arrow.py

@@ -60,7 +60,7 @@ class FixlengthArrow(torch.utils.data.Dataset):
         return img, target
 
     def __del__(self):
-        if self.reader is not None:
+        if self.reader is not None and hasattr(self.reader, 'close'):
             self.reader.close()
         if self.arrowfile is not None:
             self.arrowfile.close()

varlength_arrow.py

@@ -59,7 +59,7 @@ class VarlengthArrow(torch.utils.data.Dataset):
         return img, target
 
     def __del__(self):
-        if self.reader is not None:
+        if self.reader is not None and hasattr(self.reader, 'close'):
             self.reader.close()
         if self.arrowfile is not None:
             self.arrowfile.close()