app.py

import gradio as gr
def ping(L=3.0): return {"ok": True, "L": float(L)}
demo = gr.Interface(fn=ping, inputs=gr.Number(value=3.0, label="Span L [m]"),
                    outputs=gr.JSON(label="Result"), title="Beam Calculator (placeholder)")
if __name__ == "__main__": demo.launch()