Python, How to swap between multiple infinite loops?

Question

Could someone please point me in the right direction?

I am trying to swap between multiple infinite control loops within python. I need to kill a loop and then select a different loop upon request from an outside source(hopefully web interface), not based on an internal condition. I understand this is a vague question but I need a general point in the right direction to get me started, I have looked at exceptions, signals and threading but I am struggling to find what would be the "correct" way to do this.

Please note, I work in electronics not programming so sorry if this sounds stupid. Also if this is completely the wrong way to go about the problem could someone advise me on the correct method.

I can provide more info/explanation if someone can help me and post code if needed but I think it's pretty irrelevant at the moment due to the vagueness of the question.

Thanks

Best would be an asynchronous event loop (reactor model). Bat those are harder to write, and may require re-designing your code. — Keith
– Keith, Commented Nov 21, 2012 at 23:07

munk · Accepted Answer · 2012-11-26 15:16:36Z

2

I'm guessing you have two (or more) procedures you want to run repeatedly and allow them to be changed when the user selects a new condition. I would take advantage of Python having functions as objects and so something like this:

def f1():
    # do something
def f2():
    # do something else

func_to_run = {"user_input1": f1, "user_input2": f2}

while True:
    user_input = get_any_new_input()  # however you want to get your user input
    func_to_run[user_input]()

Edit: As Keith mentioned in the comments, get_any_new_input needs to be non-blocking. I would do this via threading. The web interface should be on a separate thread from the loops, but share a control object that the web interface will set. This could be a table in a database if you have that available. It might look something like this if you use your own lock:

L = threading.Lock()  # Shared by web ui
user_response = 'data set by web ui'
last_input = 'user_input1'

def get_any_new_input(L, last_input, user_response):
    if L.acquire([False]):
        last_input = user_response
    return last_input

edited Nov 26, 2012 at 15:16

answered Nov 21, 2012 at 22:17

munk

13.2k10 gold badges54 silver badges72 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Keith Over a year ago

That's a good idea to use function objects, but doesn't address how to make the switch. The get_any_new_input would have to be non-blocking.

Joran Beasley · Accepted Answer · 2012-11-27 17:32:48Z

1

The easiest way is probably just read some file which controls your loops ...

while True:
    #loop1
    while True:
       #do something
       with open("some.file") as f:
            if f.read() == "loop2":
                break
     #loop2
     while True:
        #do something
        with open("some.file") as f:
            if f.read() == "loop1":
                break

then just put which loop you want in "some.file" (however you want ... web interface etc)

edited Nov 27, 2012 at 17:32

answered Nov 21, 2012 at 22:06

Joran Beasley

114k13 gold badges167 silver badges187 bronze badges

Collectives™ on Stack Overflow

Python, How to swap between multiple infinite loops?

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related