How to check if a variable's value has changed

Question

If I have a variable:

var = 5

I want to detect and jump to a function when the value of the variable changes, so if var is not equal to the value it was before, I want to jump to a function.

What is the easiest way to do this?

Another example:

from datetime import datetime
import time


def dereferentie():
    currentMinute = datetime.now().minute
    checkMinute(currentMinute)

def checkMinute(currentMinute):

    #if currentMinute has changed do:
        printSomething()

def printSomething():
    print "Minute is updated"


def main():
    while (1):
        dereferentie()


if __name__ == '__main__':
    main()

Answer 1

Building on @HelloWorld's answer and @drIed's comment: A nice way would be, to wrap this into a class.

For example:

class Watcher:
    """ A simple class, set to watch its variable. """
    def __init__(self, value):
        self.variable = value
    
    def set_value(self, new_value):
        if self.variable != new_value:
            self.pre_change()
            self.variable = new_value
            self.post_change()
    
    def pre_change(self):
        pass # do stuff before variable is about to be changed
        
    def post_change(self):
        pass # do stuff right after variable has changed
        

Answer 2

I would go with a setter function which triggers your needed function.

def setValue(val):
    global globalVal
    valueChanged= g_val != val
    if valueChanged:
        preFunction()
    globalVal = val
    if valueChanged:
        postFunction()