app.py

#!/usr/bin/env python

import gradio as gr

with gr.Blocks() as demo:
    with gr.Row():
        with gr.Column():
            dropdown = gr.Dropdown(
                choices=["abc", "def", "ghi"],
                value="abc",
                allow_custom_value=False,
            )
            button = gr.Button()
        with gr.Column():
            out = gr.Textbox()

    button.click(fn=lambda x: x, inputs=dropdown, outputs=out)

if __name__ == "__main__":
    demo.queue().launch()