Tracemalloc code:

    import re
    import signal
    import tracemalloc

    class AlarmError(Exception):
        pass
    def handle_alarm(signal, frame):
        raise AlarmError
    signal.signal(signal.SIGALRM, handle_alarm)

    s1 = tracemalloc.take_snapshot()
    for _ in range(20):
        try:
            signal.alarm(1)
            re.match('(?:a|a|(?=b)){1000}', 'a'*999)
            raise RuntimeError
        except AlarmError:
            pass
    s2 = tracemalloc.take_snapshot()
    res = s2.compare_to(s1, 'lineno')
    for e in res[:10]:
        print(e)

For me, it shows almost 3 MiB allocated in re.py.