Looking inside _parse_known_args, I see some error paths doing raise ArgumentError and others calling self.error, without any apparent pattern. If they all did raise ArgumentError, that would fix this bug.

There are other calls to self.error elsewhere in the class that may be invoked from _parse_known_args, so this still leaves some paths where it may exit. In that sense, your original solution was more robust. I am honestly not sure which solution is better.

I found a duplicate with some more discussion: bpo-41255.

From the penultimate comment:

I'm not sure I like the idea of changing the exit or error methods since they have a a clear purpose and don't need to be repurposed to also include error handling. It seems to me that adding checks to self.exit_on_error in _parse_known_args to handle the missing required arguments and in parse_args to handle unknown arguments is probably a quick and clean solution.

Alternative to #27295

Backref to #85427 (@jacobtylerwalls please could you update the title to start with gh-85427?).

A