old_contents: # -*- coding: utf-8 -*-
  
  try:
      from __builtins__ import ReferenceError
  except (NameError, ImportError): # pragma: no cover
      from weakref import ReferenceError
  
  __all__ = ['ReferenceError']
  
new_contents: # -*- coding: utf-8 -*-
  import sys
  try:
      if sys.version_info[0] < 3:
          from __builtins__ import ReferenceError
      else:
          from builtins import ReferenceError
  except (NameError, ImportError): # pragma: no cover
      from weakref import ReferenceError
  
  __all__ = ['ReferenceError']
  
subject: Fix a py3 bug in reference compatibility