def __init__(
        self,
        input_key: str,
        output_key: Optional[str] = None,
        lambda_fn: Optional[Callable] = None,
        **kwargs,
    ):
        """
        Args:
            input_key: input key to use from annotation dict
            output_key: output key to use to store the result
            lambda_fn: encode function to use to prepare your data
              (for example convert chars/words/tokens to indices, etc)
            kwargs: kwargs for encode function
        """
        super().__init__(input_key, output_key)
        lambda_fn = lambda_fn or (lambda x: x)
        self.lambda_fn = functools.partial(lambda_fn, **kwargs)

        Args:
            input_key: input key to use from annotation dict
            output_key: output key to use to store the result
            lambda_fn: encode function to use to prepare your data
              (for example convert chars/words/tokens to indices, etc)
            kwargs: kwargs for encode function
        
catalyst/contrib/data/reader.py