message: In python2 itertools zip_longest is named izip_longest
diff: from gudhi import AlphaComplex, SimplexTree
  import math
  import numpy as np
  -import itertools
  import pytest
  +try:
  + # python3
  + from itertools import zip_longest
  +except ImportError:
  + # python2
  + from itertools import izip_longest as zip_longest
  __author__ = "Vincent Rouvreau"
  __copyright__ = "Copyright (C) 2016 Inria"
  @@ -114,6 +119,6 @@ def test_safe_alpha_persistence_comparison():
  diag1 = simplex_tree1.persistence()
  diag2 = simplex_tree2.persistence()
  - for (first_p, second_p) in itertools.zip_longest(diag1, diag2):
  + for (first_p, second_p) in zip_longest(diag1, diag2):
  assert first_p[0] == pytest.approx(second_p[0])
  assert first_p[1] == pytest.approx(second_p[1])
  