code: def put_shebang(f, version):
      
      if not contains_shebang(f):
          f.seek(0)
          original_text = f.read()
          f.seek(0)
          f.write(shebangs[version] + original_text)
docs: Writes a shebang to the first line of the file according to the specified
      version. (2 | 3 | default)