The documentation at https://docs.python.org/3/library/threading.html#threading.Thread.is_alive relates:

> The module function enumerate() returns a list of all alive threads.

The documentation at https://docs.python.org/3/library/threading.html#threading.enumerate relates:

> Return a list of all Thread objects currently alive. The list includes daemonic threads, dummy thread objects created by current_thread(), and the main thread.

This is a contradiction, since if the main thread has stopped, is_alive(main_thread) will return False, but it will still be included in the list returned by threading.enumerate.

Note that this is not a TOCTTOU issue. The issue is that enumerate actually includes "all alive threads, plus one [or more? I can't tell from the code] other[s]."