IndexError when creating a pure API endpoint

[jeberger]

Describe the bug

For unit testing purposes, I wanted to create a pure API endpoint, i.e. a function that could be called from gradio_client but wouldn't show in the UI. So I tried:

gr.on ([], fn = test, show_api = False)

but this throws an IndexError in set_event_trigger.

Note: this is similar to #6730 but slightly different: in #6730, passing None is expected to trigger on all changes. Here I'm attempting to never trigger from the UI and only be able to call the function with an explicit REST request.

Have you searched existing issues? 🔎

• I have searched and found no existing issues

Reproduction

import gradio as gr
import gradio_client as gc

def test():
    print ("Test!")
    return []

with gr.Blocks() as demo:
    gr.on ([], fn = test, show_api = False)
    demo.launch (prevent_thread_lock = True, server_port = 7860)

client = gc.Client ("http://127.0.0.1:7860")
client.predict (api_name = "/test")

Screenshot

No response

Logs

Traceback (most recent call last):
  File "test_gradio.py", line 9, in <module>
    gr.on ([], fn = test, show_api = False)
  File ".venv/lib/python3.11/site-packages/gradio/events.py", line 820, in on
    dep, dep_index = root_block.set_event_trigger(
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv/lib/python3.11/site-packages/gradio/blocks.py", line 784, in set_event_trigger
    if _targets[0][1] in ["change", "key_up"] and trigger_mode is None:
       ~~~~~~~~^^^
IndexError: list index out of range

System Info

Gradio Environment Information:
------------------------------
Operating System: Linux
gradio version: 5.9.1
gradio_client version: 1.5.2

------------------------------------------------
gradio dependencies in your environment:

aiofiles: 23.2.1
anyio: 4.6.2.post1
audioop-lts is not installed.
fastapi: 0.115.6
ffmpy: 0.4.0
gradio-client==1.5.2 is not installed.
httpx: 0.28.0
huggingface-hub: 0.26.3
jinja2: 3.1.4
markupsafe: 2.1.5
numpy: 2.1.3
orjson: 3.10.12
packaging: 24.2
pandas: 2.2.3
pillow: 10.4.0
pydantic: 2.10.3
pydub: 0.25.1
python-multipart: 0.0.19
pyyaml: 6.0.2
ruff: 0.8.1
safehttpx: 0.1.6
semantic-version: 2.10.0
starlette: 0.41.3
tomlkit: 0.12.0
typer: 0.15.0
typing-extensions: 4.12.2
urllib3: 2.2.3
uvicorn: 0.32.1
authlib; extra == 'oauth' is not installed.
itsdangerous; extra == 'oauth' is not installed.


gradio_client dependencies in your environment:

fsspec: 2024.10.0
httpx: 0.28.0
huggingface-hub: 0.26.3
packaging: 24.2
typing-extensions: 4.12.2
websockets: 12.0

Severity

I can work around it

[jeberger]

As a workaround, I'm currently using a hidden inactive button as a trigger:

gr.on (gr.Button (render = False).click, fn = test, show_api = False)

[abidlabs]

We're thinking about how to make this exact use case easier, stay tuned.