old_contents: $py_copyright
  
  def _main():
      print("Hello from $project_name")
  
  if __name__ == "__main__":
      _main()
  
new_contents: #!/usr/bin/env python
  $py_copyright
  from __future__ import print_function
  
  def _main():
      print("Hello from $project_name")
  
  if __name__ == "__main__":
      _main()
  
subject: Add shebang and future import