u"""
        Concrete method of Subject.unregister().
        Unregister observers as an argument to self.observers.

def unregister(self, observers):
        u"""
        Concrete method of Subject.unregister().
        Unregister observers as an argument to self.observers.
        """

        if isinstance(observers, list) or isinstance(observers, tuple):
            for observer in observers:
                try:
                    index = self._observers.index(observer)
                    self._observers.remove(self._observers[index])
                except ValueError:
                    # logging
                    print('{observer} not in list...'.format(observer))

        elif isinstance(observers, base.Observer):
            try:
                index = self._observers.index(observers)
                self._observers.remove(self._observers[index])
            except ValueError:
                # logging
                print('{observer} not in list...'.format(observers))

        else:
            err_message = ('ConfigReader.register support'
                           'ListType, TupleType and {observer} Object.'
                           ''.format(base.Observer.__name__)
                           )

            raise ValueError(err_message)