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

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.value != new_value:
            self.pre_change()
            self.variable = new_value
            self.post_change()

    def pre_change(self):
        # do stuff before variable is about to be changed

    def post_change(self):
        # do stuff right after variable has changed