def submatrix(self, col_slice, row_slice):
     col_slice = to_slice(col_slice)
     row_slice = to_slice(row_slice)
     rows = [ row[col_slice] for row in self._orig_buttons[row_slice] ]
     return ButtonMatrixElement(rows=rows)
 def subdisplay(self, char_slice):
     char_slice = to_slice(char_slice)
     return SubDisplayElement(sub_display_slice=char_slice, parent_display=self)