old_contents: Python 3.4.0 (default, Apr 11 2014, 13:05:11) 
  [GCC 4.8.2] on linux
  Type "copyright", "credits" or "license()" for more information.
  >>> def d = 3
  SyntaxError: invalid syntax
  >>> d = 3
  >>> d
  3
  >>> 
  
new_contents: Python 3.4.0 (default, Apr 11 2014, 13:05:11) 
  [GCC 4.8.2] on linux
  Type "copyright", "credits" or "license()" for more information.
  >>> def d = 3
  SyntaxError: invalid syntax
  >>> d = 3
  >>> d + 1
  
subject: test modify