diff --git a/internetarchive/item.py b/internetarchive/item.py
index <HASH>..<HASH> 100644
--- a/internetarchive/item.py
+++ b/internetarchive/item.py
@@ -337,6 +337,8 @@ class Item(object):
                                      ignore_bucket=ignore_bucket)
         request = Request('PUT', endpoint, headers=headers)
         # TODO: Add support for multipart.
+        # `contextlib.closing()` is used to make StringIO work with 
+        # `with` statement.
         with closing(local_file) as data:
             request.data = data.read()
         prepped_request = request.prepare()
Added comment about why we are using `contextlib.closing()` in the `upload_file()` method (StringIO).