code: def realpath(*args):
      
      if None in args:
          return None
      return os.path.realpath(
          os.path.expandvars(os.path.expanduser(os.path.join(*args))))
docs: Join all args and return the real path, rooted at /.
  
      Expands ``~`` and environment variables such as :envvar:`$HOME`.
  
      Returns ``None`` if any of the args is none.