update_cells not working as expected - gspread

Question

I have written this function:
def duplicate_sheet1(wb, title=None):
if title is None:
title = wb.sheet1.title + ' DUPLICATE'
wb._sheet_list = [wb.sheet1]
wb.add_worksheet(title, wb.sheet1.row_count, wb.sheet1.col_count)
wb._sheet_list = wb._sheet_list[::-1]
wb._sheet_list[0].update_cells(wb._sheet_list[1]._fetch_cells())
...everything works as expected upon inspection with a debugger except update_cells, when I _fetch_cells for worksheet 0 after running the code, the sheet is empty.

Answer 1

Apparently the list returned by _fetch_cells is not the same as what is expected by update_cells. This may be because _fetch_cells does not include empty cells in the returned list, update_cells may only work with a 1 or 2-D grid--I am unsure.
Here is the work-around I found, apologies as the code could could probably be improved:
def duplicate_sheet1(wb, title=None):
if title is None:
title = wb.sheet1.title + ' DUPLICATE'
wb._sheet_list = [wb.sheet1]
wb.add_worksheet(title, wb.sheet1.row_count, wb.sheet1.col_count)
wb._sheet_list = wb._sheet_list[::-1]
cell_list = build_cell_list(wb._sheet_list[0], wb._sheet_list[1])
wb._sheet_list[0].update_cells(cell_list)
def build_cell_list(new_worksheet, old_worksheet):
fetched = old_worksheet._fetch_cells()
max_row = fetched[-1].row
max_col = max([cell.col for cell in fetched])
cell_list = new_worksheet.range('A1:' + chr(max_col + 64) + str(max_row))
for cell in cell_list:
cell.value = next(
(
f.value for f in fetched
if f.col == cell.col and f.row == cell.row
),
'',
)
return cell_list