old_contents: # -*- coding: utf-8 -*-
  
  import sys
  
  IS_PY2 = sys.version_info[0] == 2
  IS_PY3 = sys.version_info[0] == 3
  
  
  if IS_PY2:
      from StringIO import StringIO
      unicode, str, bytes, basestring = unicode, str, str, basestring
  elif IS_PY3:
      from io import StringIO
      unicode, str, bytes, basestring = str, bytes, bytes, str
  else:
      raise NotImplementedError('welcome to the future, I guess. (report this)')
  
new_contents: # -*- coding: utf-8 -*-
  
  import sys
  
  IS_PY2 = sys.version_info[0] == 2
  IS_PY3 = sys.version_info[0] == 3
  
  
  if IS_PY2:
      from StringIO import StringIO
      unicode, str, bytes, basestring = unicode, str, str, basestring
  elif IS_PY3:
      from io import StringIO
      unicode, str, bytes, basestring = str, bytes, bytes, str
  else:
      raise NotImplementedError('welcome to the future, I guess. (report this)')
  
  
  def make_sentinel(name, var_name=None):
      class Sentinel(object):
          def __init__(self):
              self.name = name
              self.var_name = var_name
          def __repr__(self):
              if self.var_name:
                  return self.var_name
              return '%s(%r)' % (self.__class__.__name__, self.name)
          if var_name:
              def __reduce__(self):
                  return self.var_name
      return Sentinel()
  
subject: add sentinel utility thing