Go backwards in time when something went wrong

atomic_contextmanager.py

import os
import sys
import inspect
import signal
from contextlib import contextmanager

def _kill_self(signum, frame):
    os._exit(0)

@contextmanager
def atomic():
    ppid = os.getpid()
    cpid = os.fork()
    if cpid:
        signal.signal(signal.SIGUSR1, _kill_self)
        os.waitpid(cpid, 0)
        signal.signal(signal.SIGUSR1, signal.SIG_DFL)  # ignore signal again
        sys.settrace(lambda *a, **k:None)
        frame = inspect.currentframe().f_back.f_back
        def raiser(*a): raise RuntimeError
        frame.f_trace = raiser
        try:
            yield
        except RuntimeError:
            return
    try:
        yield
    except Exception:
        # rollback: we exit
        os._exit(0)
    else:
        # all good: tell state-preserved parent to kill itself
        os.kill(ppid, signal.SIGUSR1)

x = 23
with atomic():
    x += 1
    1/0
print(x)