How to make a python context manager catch a SIGINT or SIGTERM signal

Question

I stream data using context manager to close the connection when the program exits. I run my program as a daemon in the background.

How can I make the context manager handle the case when the daemon is interrupted by a SIGINT or SIGTERM or any interrupt signal sent by the kill command ?

I am running Python 3 on a Raspberry Pi and Ubuntu.

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I have seen this: How do I capture SIGINT in Python? Which is helpful, but I am not sure how to use that with python's context manager ? ie. let's say I have an object that I have built as a context manager:

class Sensor:

    def __init__(self, name: str):
        self.name = name

    def __enter__(self):
        self._connect()
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.close()

I use that object inside a script that is run as daemon. Is there a pythonic way to specify to specify that the __exit__ function has to be called also on SIGINT and SIGTERM exceptions ?

Answer 1

You could create a internal method (e.g. _handle_interrupt) for your context manager that calls sys.exit() and register it as a signal handler once __enter__ is called:

class Sensor:

    def __init__(self, name: str):
        self.name = name

    def _handle_interrupt(self):
       sys.exit()  # will trigger a exception, causing __exit__ to be called

    def __enter__(self):
        signal.signal(signal.SIGINT, self._handle_interrupt)
        signal.signal(signal.SIGTERM, self._handle_interrupt)
        self._connect()
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.close()

You should also have a look at PEP 419, which could be helpful for your setup. As for your requirements with regards to threading it is hard to tell without more information.