Appends :attr:`value` to the list named :attr:`list_name`.

def append(self, list_name, value):
        """Appends :attr:`value` to the list named :attr:`list_name`."""
        with self.lock:
            l = self.lists.get(list_name)
            if l:
                l.append(value)
            else:
                l = [value]
            self.lists[list_name] = l