old_contents: # coding=utf-8
  import sys
  
  PY2 = sys.version_info[0] == 2
  if not PY2:
      text_type = str
      string_types = (str,)
      unichr = chr
  else:
      text_type = unicode
      string_types = (str, unicode)
      unichr = unichr
new_contents: # coding=utf-8
  """
  Compatibility helpers for Python 2 and 3.
  
  See: http://lucumr.pocoo.org/2013/5/21/porting-to-python-3-redux/
  
  """
  import sys
  
  PY2 = sys.version_info[0] == 2
  if not PY2:
      text_type = str
      string_types = (str,)
      unichr = chr
  else:
      text_type = unicode
      string_types = (str, unicode)
      unichr = unichr
subject: Add compat.py explanation.