I'm not sure if I'm doing something wrong or your aiohttp example is wrong! Seems backoff decorator doesn't catch aiohttp exceptions automatically and you need to raise the error manually:

@backoff.on_exception(backoff.expo,
                      aiohttp.ClientError,
                      max_tries=4)
async def get_url(url):
    async with aiohttp.ClientSession() as session:

in release notes and the doc

From the docs

The factor option is used to grow the delay exponentially. For example, a value of 2 will cause the delay to double each time. A value of 3 will cause the delay to triple each time. Fractional factors (e.g. 1.5) are also allowed.

The following formula is used to calculate delay using the factor:

delay = delay * Math.pow(factor, attemptNum)

(default: 0)

Th