def flexible(self):
        """
        A node is flexible if its size isn't (explicitly or implicitly)
        determined.
        """
        if self.fixed:
            return False
        return all((any(gc.flexible for gc in c) or c.is_leaf) for c in self)

        A node is flexible if its size isn't (explicitly or implicitly)
        determined.
        
libqtile/layout/plasma.py