Efficient way of having a function only execute once in a loop

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I would use a decorator on the function to handle keeping track of how many times it runs.

def run_once(f):
    def wrapper(*args, **kwargs):
        if not wrapper.has_run:
            wrapper.has_run = True
            return f(*args, **kwargs)
    wrapper.has_run = False
    return wrapper


@run_once
def my_function(foo, bar):
    return foo+bar

Now my_function will only run once. Other calls to it will return None. Just add an else clause to the if if you want it to return something else. From your example, it doesn’t need to return anything ever.

If you don’t control the creation of the function, or the function needs to be used normally in other contexts, you can just apply the decorator manually as well.

action = run_once(my_function)
while 1:
    if predicate:
        action()

This will leave my_function available for other uses.

Finally, if you need to only run it once twice, then you can just do

action = run_once(my_function)
action() # run once the first time

action.has_run = False
action() # run once the second time

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