PL/Python exception bug

gistfile1.txt

create function python_exception_bug()
returns void as $$
    raise plpy.spiexceptions.InvalidParameterValue()
$$ language 'plpython3u';

create function python_exception_sql()
returns text as $$
begin
    select python_exception_bug();
    return 'cannot happen';
exception when invalid_parameter_value then
    return 'expected behavior';
when others then
    return 'this is a bug';
end
$$ language 'plpgsql';