gradio launch() — the call that turns your Blocks into a running web app

$ import gradio as gr, json, urllib.request

def answer(question):
    return "42, obviously"

demo = gr.Interface(
    answer,
    inputs=gr.Textbox(label="question", placeholder="Ask anything"),
    outputs=gr.Textbox(label="answer"),
    title="Deep Thought",
    examples=[["What is the answer to everything?"]],
)
app, local_url, share_url = demo.launch(server_port=7861, prevent_thread_lock=True)
print("app class:", type(app).__module__ + "." + type(app).__name__)
print("local_url:", local_url, "| share_url:", share_url)
info = json.load(urllib.request.urlopen("http://127.0.0.1:7861/gradio_api/info"))
print("named endpoints:", list(info["named_endpoints"].keys()))

* Running on local URL:  http://127.0.0.1:7861
* To create a public link, set `share=True` in `launch()`.
app class: gradio.routes.App
local_url: http://127.0.0.1:7861/ | share_url: None
named endpoints: ['/answer']

Verified on gradio 6.27.0 (Python 3.12). The unpacked return: app is a live FastAPI (gradio.routes.App), share_url is None without share=True. The browser shows the Deep Thought title, a Textbox 'question' (placeholder 'Ask anything'), Submit, a Textbox 'answer', the example row and Clear/Flag buttons. /gradio_api/info is the machine-readable API index — the endpoint is named after the function, /answer, not /predict.

$ import gradio as gr

def caption(img, conf):
    return f"a {['dim','moody','bright'][min(int(conf*3),2)]} image"

demo = gr.Interface(
    caption,
    inputs=[gr.Image(label="image"), gr.Slider(0, 1, value=0.5, step=0.1, label="confidence")],
    outputs=gr.Textbox(label="caption", lines=2),
)
app, local, public = demo.launch(prevent_thread_lock=True, share=True)
print("CAPTURED local:", local)
print("CAPTURED share:", public)
demo.close()

* Running on local URL:  http://127.0.0.1:7860
* Running on public URL: https://25f4dae8d27c9b8019.gradio.live

This share link is temporary and will last for up to 1 week (best effort). For free permanent hosting and GPU upgrades, run `gradio deploy` from the terminal in the working directory to deploy to Hugging Face Spaces (https://huggingface.co/spaces)
CAPTURED local: http://127.0.0.1:7860/
CAPTURED share: https://25f4dae8d27c9b8019.gradio.live
Closing server running on port: 7860
Killing tunnel 127.0.0.1:7860 <> https://25f4dae8d27c9b8019.gradio.live

Ran for real on 6.27.0: share=True downloads an frpc binary, tunnels localhost to a random *.gradio.live subdomain and prints the one-week caveat. demo.close() tears the tunnel down. Rendered UI: Image input 'image' plus Slider 'confidence' on the left, Textbox 'caption' (2 lines) on the right. Your public label is the 16-hex chunk before .gradio.live — anyone holding the URL reaches your machine until the process dies.

$ import gradio as gr, urllib.request, urllib.parse, http.cookiejar

def answer(question):
    return "42, obviously"

demo = gr.Interface(answer, gr.Textbox(label="question"), gr.Textbox(label="answer"))
demo.launch(server_port=7861, prevent_thread_lock=True, quiet=True, auth=("admin", "s3cret"))

cj = http.cookiejar.CookieJar()
op = urllib.request.build_opener(urllib.request.HTTPCookieProcessor(cj))
try:
    op.open("http://127.0.0.1:7861/gradio_api/info")
except Exception as e:
    print("pre-login /gradio_api/info:", e)
r = op.open("http://127.0.0.1:7861/login",
            data=urllib.parse.urlencode({"username": "admin", "password": "s3cret"}).encode())
print("POST /login:", r.status)
r2 = op.open("http://127.0.0.1:7861/gradio_api/info")
print("post-login /gradio_api/info:", r2.status)

pre-login /gradio_api/info: HTTP Error 401: Unauthorized
POST /login: 200
post-login /gradio_api/info: 200

Verified on 6.27.0. auth= fronts the app with a login page: API routes 401 until you POST the credentials to /login, which sets an HttpOnly session cookie. Basic-auth headers are rejected — script it by POSTing /login and reusing the cookie jar (curl -c/-b cookies.txt). A wrong password returns HTTP 400, not a retry loop. quiet=True silenced the banner; the UI is the same Textbox 'question' → Textbox 'answer' demo behind the wall.

$ import gradio as gr

def reverse(text):
    return text[::-1]

with gr.Blocks() as demo:
    t_in = gr.Textbox(label="prompt")
    btn = gr.Button("Reverse")
    t_out = gr.Textbox(label="reversed")
    btn.click(reverse, t_in, t_out)

demo.launch(server_name="0.0.0.0", server_port=7861, prevent_thread_lock=True)

* Running on local URL:  http://0.0.0.0:7861
* To create a public link, set `share=True` in `launch()`.

Blocks app, verbatim run on 6.27.0: Textbox 'prompt', Button 'Reverse', Textbox 'reversed' in one column. server_name='0.0.0.0' binds every interface so colleagues on the LAN reach http://<your-ip>:7861 — the printed 0.0.0.0 is not the address you hand them. Omit server_port and launch() starts at 7860, stepping forward when occupied: in my probe a second demo auto-landed on 7861 while the first held 7860.

$ import gradio as gr

a = gr.Interface(lambda x: x, gr.Textbox(), gr.Textbox())
a.launch(server_port=7860, prevent_thread_lock=True, quiet=True)

b = gr.Interface(lambda t: t.upper(), gr.Textbox(label="text"), gr.Textbox(label="shout"))
app_b, url_b, _ = b.launch(prevent_thread_lock=True)
print("SECOND DEMO URL:", url_b)

c = gr.Interface(lambda t: t[::-1], gr.Textbox(label="text"), gr.Textbox(label="reversed"))
print("BEGIN-PRINT")
print(c.launch(prevent_thread_lock=True, quiet=True))
print("END-PRINT")
c.close(); a.close(); b.close()

* Running on local URL:  http://127.0.0.1:7861
* To create a public link, set `share=True` in `launch()`.
SECOND DEMO URL: http://127.0.0.1:7861/
BEGIN-PRINT

END-PRINT
Closing server running on port: 7862
Closing server running on port: 7860
Closing server running on port: 7861

Three launches, one output, verbatim on 6.27.0. a quietly holds 7860; b (no server_port) auto-steps to 7861 and unpacked url_b confirms it; c then lands on 7862 — visible in the closing order (c=7862, a=7860, b=7861). And print(c.launch(...)) emits an empty line: the return tuple's class, TupleNoPrint, prints nothing by design to keep notebooks clean. Two demos ran side by side on different ports with zero configuration.