Struggling to append dataframe to existing .xlsx file in Python

Question

I am trying to append a dataframe to an existing excel spreadsheet, but I am having trouble appending it to an existing SHEET (my excel file only has one sheet, titled "Sheet1," that contains the existing dataset).

    with pd.ExcelWriter(xlsx_path, mode="a", engine="openpyxl",sheet_name="Sheet1",if_sheet_exists="overlay") as writer:
          transfer.to_excel(writer,header=None,index=False)

When I use the aforementioned code, when I open the existing spreadsheet, the new data from the dataframe I requested to be appended via the to_excel function appears in a separate sheet, entitled "Sheet 11." Can someone elucidate why this is occurring? How can I just get the new data from the dataframe to appear at the bottom of the existing spreadsheet in Sheet1?

Thanks!

Refer to notes written above.

Answer 1

I dont know why the data is appended to 'Sheet11', however 'sheet_name=' is not an attribute in ExcelWriter so you should get a warning about that. The attribute should be used with 'to_excel'.
You'll need to state what row to append from otherwise the new data will start from row 1 over-writting any existing data. You can get the max row for the sheet and use that.

sheet_to_update = 'Sheet1'
with pd.ExcelWriter(xlsx_path,
                    mode="a",
                    engine="openpyxl",
                    if_sheet_exists="overlay") as writer:
    transfer.to_excel(writer,
                header=None,
                index=False,
                sheet_name=sheet_to_update,
                startrow=writer.sheets[sheet_to_update].max_row)