convert xlwt Workbook instance to an xlrd instance for reading

def workbook_to_reader(xlwt_wb):
    """
        convert xlwt Workbook instance to an xlrd instance for reading
    """
    _xlrd_required()
    fh = BytesIO()
    xlwt_wb.save(fh)
    # prep for reading
    fh.seek(0)
    return xlrd.open_workbook(file_contents=fh.read())