<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def copy(self, filename: Optional[PathLike] = None) -> 'AnnData': """Full copy, optionally on disk."""

        if not self.isbacked:
            return AnnData(self._X.copy() if self._X is not None else None,
                           self._obs.copy(),
                           self._var.copy(),
                           # deepcopy on DictView does not work and is unnecessary
                           # as uns was copied already before
                           self._uns.copy() if isinstance(self._uns, DictView) else deepcopy(self._uns),
                           self._obsm.copy(), self._varm.copy(),
                           raw=None if self._raw is None else self._raw.copy(),
                           layers=self.layers.as_dict(),
                           dtype=self._X.dtype.name if self._X is not None else 'float32')
        else:
            if filename is None:
                raise ValueError(
                    'To copy an AnnData object in backed mode, '
                    'pass a filename: `.copy(filename=\'myfilename.h5ad\')`.')
            if self.isview:
                self.write(filename)
            else:
                from shutil import copyfile
                copyfile(self.filename, filename)
            return AnnData(filename=filename)