code: def copy_fs_if_newer(
      src_fs,  # type: Union[FS, Text]
      dst_fs,  # type: Union[FS, Text]
      walker=None,  # type: Optional[Walker]
      on_copy=None,  # type: Optional[_OnCopy]
      workers=0,  # type: int
  ):
      # type: (...) -> None
      
      return copy_dir_if_newer(
          src_fs, "/", dst_fs, "/", walker=walker, on_copy=on_copy, workers=workers
      )
docs: Copy the contents of one filesystem to another, checking times.
  
      If both source and destination files exist, the copy is executed
      only if the source file is newer than the destination file. In case
      modification times of source or destination files are not available,
      copy file is always executed.
  
      Arguments:
          src_fs (FS or str): Source filesystem (URL or instance).
          dst_fs (FS or str): Destination filesystem (URL or instance).
          walker (~fs.walk.Walker, optional): A walker object that will be
              used to scan for files in ``src_fs``. Set this if you only want
              to consider a sub-set of the resources in ``src_fs``.
          on_copy (callable):A function callback called after a single file copy
              is executed. Expected signature is ``(src_fs, src_path, dst_fs,
              dst_path)``.
          workers (int): Use ``worker`` threads to copy data, or ``0`` (default) for
              a single-threaded copy.