Question

Is there some way to call a function each-time the value of a variable changes, in python?

Something like a listener, perhaps?

Specifically, I’m referring to the case where
only the variable is shared
between scripts like a GAE-Session. (Which uses Cookies, Memcache, etc to share data)

Example:
ScriptA & ScriptB, share a session variable. When Script B changes it, SctiptA has to call a method to handle that change.

Answer 1

Use properties. Only mutable values can change to begin with.

class Something(object):
    @property
    def some_value(self):
        return self._actual
    @some_value.setter
    def some_value(self, value):
        print ("some_value changed to", value)
        self._actual = value