playwright force useragent for headless mode

How can I force the useragent in playwright python?

https://playwright.dev/python/docs/emulation#user-agent

def run(playwright):
    """ config for browser """
    browser = playwright.chromium.launch(channel='msedge', headless=False)
    context = browser.new_context(
        user_agent="Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/116.0.0.0 Safari/537.36 Edg/116.0.1938.81"
    )
    return browser


with sync_playwright() as p:
    browser = run(p)
    # some info
    log.info(f"name:{browser.browser_type.name}, exe_path:{browser.browser_type.executable_path}, version:{browser.version}")
    page = browser.new_page()
    log.info(f"useragent:{page.evaluate('navigator.userAgent')}")
    page.goto(dat['url'])
    :

but useragent in headlessmode is always: useragent:Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/116.0.1938.81 Safari/537.36 HeadlessEdg/116.0.1938.81

Solution

new_page() needs to be called on the context you've created with the user agent, not the browser:

from playwright.sync_api import sync_playwright

ua = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/116.0.0.0 Safari/537.36 Edg/116.0.1938.81"

with sync_playwright() as p:
    browser = p.chromium.launch()
    page = browser.new_page()
    context = browser.new_context(user_agent=ua)
    page = context.new_page()
    assert page.evaluate("navigator.userAgent") == ua

If you really want to use run(), you can:

def run(playwright):
    # ...
    return context, browser

with sync_playwright() as p:
    context, browser = run(p)
    page = context.new_page()
    # ...