This threw a deprecated warning in Python 3.8, but now has been removed entirely in Python 3.9. I manually changed it to is_alive() and no issues so far. Should work with any Python 3.5+ versions since it's been there since, with the same functionality as isAlive().
https://github.com/fkie/multimaster_fkie/blob/52f3250f5b5e87ae988260d67346a32d2ff92382/fkie_master_discovery/src/fkie_master_discovery/master_monitor.py#L596
This threw a deprecated warning in Python 3.8, but now has been removed entirely in Python 3.9. I manually changed it to is_alive() and no issues so far. Should work with any Python 3.5+ versions since it's been there since, with the same functionality as isAlive().