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]."

The following example comes from IRC user ztane:

> import threading, time
>
> main_thread = threading.current_thread()
> 
> def foo():
>     time.sleep(10)
>     print(main_thread.is_alive())
>     print(list(threading.enumerate()))
> 
> t = threading.Thread(target=foo)
> t.start()

False
[<_MainThread(MainThread, stopped 140040101766976)>, <Thread(Thread-1, started 140040068695808)>]

New changeset 7bef7a180da56e0399f4dec2c992bb101470fc73 by Miss Islington (bot) in branch '3.10':
bpo-25821: Fix inaccuracy in threading.enumerate/is_alive documentation (GH-23192) (#26035)
https://github.com/python/cpython/commit/7bef7a180da56e0399f4dec2c992bb101470fc73

New changeset bde14f7fbd5f11bb40d9c314bd74eaa231236c6b by Miss Islington (bot) in branch '3.9':
bpo-25821: Fix inaccuracy in threading.enumerate/is_alive documentation (GH-23192) (#26036)
https://github.com/python/cpython/commit/bde14f7fbd5f11bb40d9c314bd74eaa231236c6b