Python trap routine

Question

Alright so for a living I program ABB industrial robots, and the programming language we use is called Rapid.

One really cool thing I can do in Rapid is called a trap routine. And it's like a while loop but instead of looping through the whole loop before it checks a condition it will break literally as soon as the event its waiting for happens.

I suppose it is similar to an event listener in javascript. It's like it runs in the background of the normal program. I want to do this in python.

I have little formal CS education so I'm not exactly sure what this concept is. Sorry if it's a bit vague I'm not really sure how to ask it in a clear way.

Answer 1

Like most languages, so does Python handle system signals by using handler functions. For more details, take a look at the Signals chapter which talks about receiving and sending signals, with examples e.g. here.

In short, you can bind a function to one or more signals:

>>> import signal
>>> import sys
>>> import time
>>> 
>>> # Here we define a function that we want to get called.
>>> def received_ctrl_c(signum, stack):
...     print("Received Ctrl-C")
...     sys.exit(0)
... 
>>> # Bind the function to the standard system Ctrl-C signal.
>>> handler = signal.signal(signal.SIGINT, received_ctrl_c)
>>> handler
<built-in function default_int_handler>
>>> 
>>> # Now let’s loop forever, and break out only by pressing Ctrl-C, i.e. sending the SIGINT signal to the Python process.
>>> while True:
...     print("Waiting…")
...     time.sleep(5)
... 
Waiting…
Waiting…
Waiting…
^CReceived Ctrl-C

In your specific case, find out which signal(s) the robot sends to your Python process (or whichever process listens to signals) and then act on them as shown above.