old_contents: """
  The :mod:`ast` module contains the shims which implement AST classes
  missing in versions of Python earlier than the latest one pyparser targets.
  """
  
  from __future__ import absolute_import, division, print_function, unicode_literals
  from ast import *
  import sys
  
  if sys.version_info <= (2, 6):
      class DictComp(expr):
          _fields = ('key', 'value', 'generators')
  
      class Set(expr):
          _fields = ('elts',)
  
      class SetComp(expr):
          _fields = ('elt', 'generators')
  
new_contents: """
  The :mod:`ast` module contains the shims which implement AST classes
  missing in versions of Python earlier than the latest one pyparser targets.
  """
  
  from __future__ import absolute_import, division, print_function, unicode_literals
  from ast import *
  import sys
  
  if sys.version_info <= (2, 6):
      class DictComp(expr):
          _fields = ('key', 'value', 'generators')
  
      class Set(expr):
          _fields = ('elts',)
  
      class SetComp(expr):
          _fields = ('elt', 'generators')
  
  if sys.version_info >= (3,):
      class Repr(expr):
          _fields = ('value',)
  
      class Exec(expr):
          _fields = ('body', 'globals', 'locals')
  
      class Print(expr):
          _fields = ('dest', 'values', 'nl')
  
      class TryExcept(stmt):
          _fields = ('body', 'handlers', 'orelse')
  
subject: Update ast.shim for Python 3.