python python-3.x playwright playwright-python

ERROR:"It looks like you are using Playwright Sync API inside the asyncio loop. Please use the Async API instead."

I have this setup

File 1

from playwright.sync_api import sync_playwright


class A:
   def __init__(self,login_dict):
       self.start = sync_playwright().start()
       self.browser = self.start.chromium.launch()
       self.context = self.browser.new_context()
       self.page = self.context.new_page()
       self.login_dict = login_dict

File 2

import file_1.py

class B(A):
    def __init__(self):
       super().__init__()

from file_1 import A
from file_2 import B

a = A(some_login_dict)
b = B()

I get this error at the super init of B class

It looks like you are using Playwright Sync API inside the asyncio loop. Please use the Async API instead.

I do not understand why is this happening, can someone explain? Is there a way to avoid this?

Solution

The files and classes in your code are obscuring the root cause. Nonetheless, it's good to see your intended use case, since you'd normally start Playwright with a with context manager, which isn't as obvious in the class setup.

The minimal trigger is simply starting Playwright's sync API twice, which it wasn't designed to do:

from playwright.sync_api import sync_playwright  # 1.48.0


browser = sync_playwright().start().chromium.launch()
browser = sync_playwright().start().chromium.launch()  # raises 'It looks like...'

The error message is not very clear.

The solution is to only .start() Playwright once for the application:

from playwright.sync_api import sync_playwright


sync_playwright = sync_playwright().start()

browser = sync_playwright.chromium.launch()
browser = sync_playwright.chromium.launch()

In your code, the error occurs when you initialize both A() and B() (removing one initializer or the other works).

Since you're working with classes, you can move playwright = sync_playwright().start() to the module-level scope of a shared, one-off module, which is then imported from any other file that needs to launch a browser.

An alternative approach is to use the async API, which doesn't seem to mind being started multiple times:

import asyncio
from playwright.async_api import async_playwright


async def run():
    pw1 = await async_playwright().start()
    pw2 = await async_playwright().start()
    browser1 = await pw1.chromium.launch()
    browser2 = await pw2.chromium.launch()
    page1 = await browser1.new_page()
    page2 = await browser2.new_page()
    await page1.goto("https://www.example.com")
    await page2.goto("https://en.wikipedia.org")
    print(await page1.title())
    print(await page2.title())
    await pw1.stop()
    await pw2.stop()


asyncio.run(run())

Remember to clean up with .stop() when not using context-managed Playwright.