def __init__(self, optimizer_key: str = None):
        """
        Args:
            optimizer_key: which optimizer key to use
                for learning rate scheduling
        """
        super().__init__()
        self.init_lr = 0
        self.optimizer_key = optimizer_key
        self.optimizer = None

        Args:
            optimizer_key: which optimizer key to use
                for learning rate scheduling
        
catalyst/callbacks/scheduler.py