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Many __del__ methods expect that builtins are existing at the time of executing. But when the object survives until the builtins module is wiped, __del__ will fail with unexpected AttributeError (see issue19021 for example). We can change __del__'s in the stdlib to not use non-cached builtins, but third party code will be broken.
Perhaps we should special case shutdown of the builtins module. E.g. reset it to initial value (all initial members of the builtins module are immutable and can't create resource loops) instead wiping.