def _instantiate(cls, params):
    """
    Helper to instantiate Attention classes from parameters. Warns in log if parameter is not supported
    by class constructor.

    :param cls: Attention class.
    :param params: configuration parameters.
    :return: instance of `cls` type.
    """
    sig_params = inspect.signature(cls.__init__).parameters
    valid_params = dict()
    for key, value in params.items():
        if key in sig_params:
            valid_params[key] = value
        else:
            logger.debug('Type %s does not support parameter \'%s\'' % (cls.__name__, key))
    return cls(**valid_params)