code: def get_default_shell():
      
      if is_windows():
          return 'cmd.exe'
      else:
          import pwd
          import getpass
  
          if 'SHELL' in os.environ:
              return os.environ['SHELL']
          else:
              username = getpass.getuser()
              shell = pwd.getpwnam(username).pw_shell
              return shell
docs: return the path to the default shell for the current user.