import tensorflow as tf

    :return: [batch_size, window_size] boolean tensor mask.
    """
    return tf.logical_not(tf.sequence_mask(before_padding, maxlen=window_size))


def _right_mask(after_padding, window_size):
    """Same as above, but for right-padded vectors."""
    return tf.sequence_mask(window_size - after_padding, maxlen=window_size)


class WindowFeatures(object):
    """Helper for dealing with window-like raw features.

    In particular, this class generates concatenated "dflux_dt" values, and has a masking
