Function trigger when a variable change

Question

I'm trying to write a single function that turn to true when a variable changes. The script should put the variable in a list and check if it changes. Now, I need to call the function in another loop, so the script have to do one cicle when invoked for i in range(0, 1) Anyway the function doesn't work and the output is always false...any suggestions?
(NOOB)

def change():
    v1 = []
    for i in range(0, 1):
        v1.insert(0, get.value()) #get.value gave a value when invoked
        if len(v1) > 2:
            if v1[0] != v1[1]:
                v1.clear()
                v1.insert(0, get.value())
                return True
            else:
                return False

Why? Are you expecting this to run in a separate thread? Otherwise, how can this possibly work? Do you expect this to loop forever until the variable changes? — Tim Roberts
– Tim Roberts, Commented Jun 15, 2022 at 21:36
yes, the second loop works until the function turns to true. — Francesco Battisti
– Francesco Battisti, Commented Jun 15, 2022 at 21:39

Tim Roberts · Accepted Answer · 2022-06-15 21:47:35Z

1

You've made this harder than it needs to be. Just store the value you know and wait for it to change.

def change():
    v1 = get.value()
    while get.value() == v1:
        time.sleep(0.5)
    return True

You need the sleep in there, otherwise this will consume 100% of the CPU and your other code won't run. Remember this ONLY works in a thread, which means it's probably not what you really need.

answered Jun 15, 2022 at 21:47

Tim Roberts

55.3k4 gold badges28 silver badges41 bronze badges

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

Comments

Jake Stevens-Haas · Accepted Answer · 2022-06-15 22:10:01Z

You can use a decorator factory to freeze values:

from functools import partial


def frozen_args(val):
    def my_decorator(wrapped_func):
        return partial(wrapped_func, frozenval=val)
    return my_decorator
    

class Get:
    def __init__(self):
        self.x = 1
    def value(self):
        return self.x

get = Get()

@frozen_args(get.value())
def change(frozenval: int) -> bool:
    return get.value() != frozenval

Testing it:

>>> change()
False
>>> get.x = 3
>>> change()
True

If you ever need to reset the value in testing, remove the decorator from the function definition and use it inline when you need it:

def change(frozenval: int) -> bool:
    return get.value() != frozenval

>>> change_now = frozen_args(get.value())(change)
>>> get.x = 2
>>> change_now()
True
>>> change_now = frozen_args(get.value())(change)
>>> change_now()
False

Collectives™ on Stack Overflow

Function trigger when a variable change

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related