def add_callback(self, callback: callable):
def internal_callback(*args):<EOL><INDENT>try:<EOL><INDENT>callback()<EOL><DEDENT>except TypeError:<EOL><INDENT>callback(self.get())<EOL><DEDENT><DEDENT>self._var.trace('<STR_LIT:w>', internal_callback)<EOL>
Add a callback on change

:param callback: callable function
:return: None