Issue #15233: Python now guarantees that callables registered with the atexit

module will be called in a deterministic order.

Doc/library/atexit.rst

@@ -15,13 +15,14 @@
 
 The :mod:`atexit` module defines a single function to register cleanup
 functions.  Functions thus registered are automatically executed upon normal
-interpreter termination.  The order in which the functions are called is not
-defined; if you have cleanup operations that depend on each other, you should
-wrap them in a function and register that one.  This keeps :mod:`atexit` simple.
-
-Note: the functions registered via this module are not called when the program
-is killed by a signal not handled by Python, when a Python fatal internal error
-is detected, or when :func:`os._exit` is called.
+interpreter termination.  :mod:`atexit` runs these functions in the *reverse*
+order in which they were registered; if you register ``A``, ``B``, and ``C``,
+at interpreter termination time they will be run in the order ``C``, ``B``,
+``A``.
+
+**Note:** The functions registered via this module are not called when the
+program is killed by a signal not handled by Python, when a Python fatal
+internal error is detected, or when :func:`os._exit` is called.
 
 .. index:: single: exitfunc (in sys)
 

Misc/NEWS

@@ -32,6 +32,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #15233: Python now guarantees that callables registered with the atexit
+  module will be called in a deterministic order.
+
 - Issue #18747: Re-seed OpenSSL's pseudo-random number generator after fork.
   A pthread_atfork() child handler is used to seeded the PRNG with pid, time
   and some stack data.