The semantics of del sys.breakpointhook isn't well defined, either in PEP 553 or in the stdlib docs. However the intent is for it to act similarly to sys.displayhook and sys.excepthook, except that those aren't entirely consistent either:

Python 3.10.6 (main, Aug 11 2022, 13:49:25) [Clang 13.1.6 (clang-1316.0.21.2.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> del sys.displayhook
>>> repr(object())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
RuntimeError: lost sys.displayhook
>>> del sys.excepthook
>>> 1/0
sys.excepthook is missing
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: division by zero

del sys.displayhook produces a RuntimeError but del sys.excepthook does not (you get the original exception). This all makes sense, and in the case of del sys.breakpointhook I suppose it should act more like del sys.displayhook, which it does.

All that to say, I wonder if these behaviors should be documented in sys module documentation?

Uh oh!

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