Support empty lists being used in gr.Dataframe (#3646)

* Support empty lists being used in `gr.Dataframe`

* Update changelog

* Add empty dataframe test

---------

Co-authored-by: Abubakar Abid <abubakar@huggingface.co>

CHANGELOG.md

@@ -16,6 +16,7 @@
 - Fixed bug where chatbot does not autoscroll inside of a tab, row or column by [@dawoodkhan82](https://github.com/dawoodkhan82) in [PR 3637](https://github.com/gradio-app/gradio/pull/3637)
 - Fixed bug where textbox shrinks when  `lines` set to larger than 20 by [@dawoodkhan82](https://github.com/dawoodkhan82) in [PR 3637](https://github.com/gradio-app/gradio/pull/3637)
 - Ensure CSS has fully loaded before rendering the application, by [@pngwn](https://github.com/pngwn) in [PR 3573](https://github.com/gradio-app/gradio/pull/3573)
+- Support using an empty list as `gr.Dataframe` value, by [@space-nuko](https://github.com/space-nuko) in [PR 3646](https://github.com/gradio-app/gradio/pull/3646)
 
 ## Documentation Changes:
 

gradio/components.py

@@ -2878,6 +2878,8 @@ class Dataframe(Changeable, Selectable, IOComponent, JSONSerializable):
                 ),
             }
         if isinstance(y, (np.ndarray, list)):
+            if len(y) == 0:
+                return self.postprocess([[]])
             if isinstance(y, np.ndarray):
                 y = y.tolist()
             assert isinstance(y, list), "output cannot be converted to list"

test/test_components.py

@@ -1096,6 +1096,8 @@ class TestDataframe:
         postprocess
         """
         dataframe_output = gr.Dataframe()
+        output = dataframe_output.postprocess([])
+        assert output == {"data": [[]], "headers": []}
         output = dataframe_output.postprocess(np.zeros((2, 2)))
         assert output == {"data": [[0, 0], [0, 0]], "headers": [1, 2]}
         output = dataframe_output.postprocess([[1, 3, 5]])