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Wait for a specific element before capturing in Python with httpx

A fixed delay is a guess: too short and you capture the spinner, too long and every render pays for the worst case. wait_for_selector replaces the guess with a condition — pass a CSS selector and the render proceeds the moment a matching element is visible. The dashboard's chart, the map's tiles, the price table: name the thing you are actually waiting for, and wait for that.

Below is a complete, runnable Python program using httpx (pip install httpx). It reads your API key from the SNAPDOK_KEY environment variable — free keys take about thirty seconds and need no card.

import os
import httpx

resp = httpx.post(
    "https://snapdok.io/v1/render",
    headers={"Authorization": "Bearer " + os.environ["SNAPDOK_KEY"]},
    json={
        "url": "https://your-app.com/report/42",
        "format": "png",
        "wait_for_selector": "#chart-ready",
        "wait_until": "networkidle",
    },
    timeout=90,
)
resp.raise_for_status()

with open("ready.png", "wb") as f:
    f.write(resp.content)
print(resp.headers.get("X-Cache"), "# the settled render is cached like any other")

Selector choice is the whole game. Pick an element that appears last in your page's load sequence — a #chart-ready marker your own code adds after drawing, the final list item, the element a skeleton placeholder is replaced by. An element that exists in the initial HTML matches immediately and waits for nothing; visibility is required precisely so a pre-rendered-but-hidden node does not count as ready.

The failure mode is the feature: if the element never becomes visible within timeout, the render fails with 504 SELECTOR_TIMEOUT — not metered, and unambiguous in your logs — instead of silently shipping a half-rendered image the way an expired delay does. The sequencing composes with the other waits: navigation finishes (wait_until), then delay runs, then the selector wait begins. It works on every format, pdf_forms included.

Same endpoint, one more trick: if the page you are rendering has a form on it, adding "pdf_forms": true to a PDF render brings it back with real, fillable AcroForm fields — a PDF people can type into, not a picture of one. How that works.

Notes for httpx

httpx looks like requests but differs where it bites: it ships a 5-second default timeout, which a render that drives a real browser will blow through on heavier pages — hence the explicit timeout=90. raise_for_status() exists and behaves the same. If you are on asyncio already, the same call works with httpx.AsyncClient and await client.post(...) — the request body and headers are identical.

Response headers worth reading

Header	Meaning
`X-Cache`	HIT when an identical request rendered within 24h.
`X-RateLimit-Remaining`	Requests left in the current second.

Full parameter reference: the docs. Hard numbers on caps and timeouts: limits.

Wait for a specific element before capturing in Python with httpx

Notes for httpx

Response headers worth reading

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