print() is a function in Python 3

[Christian Clauss]

flake8 testing of https://github.com/google/compare_gan on Python 3.6.3

$ flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics

./compare_gan/src/datasets.py:86:16: F821 undefined name 'xrange'
      for i in xrange(range_start, range_end)
               ^
./compare_gan/src/gan_lib.py:198:38: E999 SyntaxError: invalid syntax
        print " [*] Training started!"
                                     ^
./compare_gan/src/image_similarity.py:296:14: F821 undefined name 'xrange'
    for k in xrange(len(power_factors)):
             ^
./compare_gan/src/simple_task_pb2.py:46:46: F821 undefined name 'unicode'
      has_default_value=False, default_value=unicode("", "utf-8"),
                                             ^
./compare_gan/src/simple_task_pb2.py:53:46: F821 undefined name 'unicode'
      has_default_value=False, default_value=unicode("", "utf-8"),
                                             ^
./compare_gan/src/gans/WGAN.py:42:35: E999 SyntaxError: invalid syntax
      print "Using Adam optimizer."
                                  ^
./compare_gan/src/gans/gans_with_penalty.py:73:35: E999 SyntaxError: invalid syntax
      print "Using Adam optimizer."
                                  ^
./compare_gan/src/gans/ops.py:141:35: E999 SyntaxError: invalid syntax
  print " [*] Spectral norm layers"
                                  ^
4     E999 SyntaxError: invalid syntax
4     F821 undefined name 'xrange'
8