'Copy an array portion to a unicode string'

def _sel_to_text(self, cell_range):

    if (not cell_range):
        return
    (row_min, row_max, col_min, col_max) = get_idx_rect(cell_range)
    if ((col_min == 0) and (col_max == (self.model().cols_loaded - 1))):
        col_max = (self.model().total_cols - 1)
    if ((row_min == 0) and (row_max == (self.model().rows_loaded - 1))):
        row_max = (self.model().total_rows - 1)
    _data = self.model().get_data()
    if PY3:
        output = io.BytesIO()
    else:
        output = io.StringIO()
    try:
        np.savetxt(output, _data[row_min:(row_max + 1), col_min:(col_max + 1)], delimiter=' DCTB ', fmt=self.model().get_format())
    except:
        QMessageBox.warning(self, _('Warning'), _('It    was    not    possible    to    copy    values    for    this    array'))
        return
    contents = output.getvalue().decode('utf-8')
    output.close()
    return contents
