[3.9] bpo-25821: Fix inaccuracy in threading.enumerate/is_alive documentation (GH-23192)

Doc/library/threading.rst

@@ -110,10 +110,11 @@ This module defines the following functions:
 
 .. function:: enumerate()
 
-   Return a list of all :class:`Thread` objects currently alive.  The list
-   includes daemonic threads, dummy thread objects created by
-   :func:`current_thread`, and the main thread.  It excludes terminated threads
-   and threads that have not yet been started.
+   Return a list of all :class:`Thread` objects currently active.  The list
+   includes daemonic threads and dummy thread objects created by
+   :func:`current_thread`.  It excludes terminated threads and threads
+   that have not yet been started.  However, the main thread is always part
+   of the result, even when terminated.
 
 
 .. function:: main_thread()

Lib/threading.py

@@ -1094,8 +1094,8 @@ def is_alive(self):
         """Return whether the thread is alive.
 
         This method returns True just before the run() method starts until just
-        after the run() method terminates. The module function enumerate()
-        returns a list of all alive threads.
+        after the run() method terminates. See also the module function
+        enumerate().
 
         """
         assert self._initialized, "Thread.__init__() not called"