♻️ add underscore to Shard class

    return NumpyDataset(X, y, w, ids, n_tasks=y.shape[1])

class Shard(object):

class _Shard(object):

  def __init__(self, X, y, w, ids):

    self.X = X

    # shard again before the next time we want this one.  So just cache as many

    # as we can and then stop.

    shard = Shard(X, y, w, ids)

    shard = _Shard(X, y, w, ids)

    shard_size = X.nbytes + ids.nbytes

    if y is not None:

      shard_size += y.nbytes