def add_sheet(self, sheetname, cell_overwrite_ok=False):
from arelle import Worksheet, Utils
if not isinstance(sheetname, str):
sheetname = sheetname.decode(self.encoding)
if not Utils.valid_sheet_name(sheetname):
raise Exception("invalid worksheet name %r" % sheetname)
lower_name = sheetname.lower()
if lower_name in self.__worksheet_idx_from_name:
raise Exception("duplicate worksheet name %r" % sheetname)
self.__worksheet_idx_from_name[lower_name] = len(self.__worksheets)
self.__worksheets.append(Worksheet(sheetname, self, cell_overwrite_ok))
return self.__worksheets[-1]
