In Python web scraping, how do I optimize performance?

# Example of using asyncio for asynchronous web scraping
import aiohttp
import asyncio

async def fetch(url):
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as response:
            return await response.text()

async def main(urls):
    tasks = [fetch(url) for url in urls]
    results = await asyncio.gather(*tasks)
    return results

urls = ['http://example.com', 'http://example.org']
loop = asyncio.get_event_loop()
output = loop.run_until_complete(main(urls))
print(output)