message: Import collections as a module, rather than defaultdict
  This was causing a lint error.
diff: @@ -18,7 +18,7 @@ from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  -from collections import defaultdict
  +import collections
  import numpy as np
  import six
  @@ -58,7 +58,7 @@ class HDF5Matrix(object):
  Returns:
  An array-like HDF5 dataset.
  """
  - refs = defaultdict(int)
  + refs = collections.defaultdict(int)
  def __init__(self, datapath, dataset, start=0, end=None, normalizer=None):
  if h5py is None:
  