how to convert xls to xlsx

You need to have win32com installed on your machine. Here is my code:

import win32com.client as win32
fname = "full+path+to+xls_file"
excel = win32.gencache.EnsureDispatch('Excel.Application')
wb = excel.Workbooks.Open(fname)

wb.SaveAs(fname+"x", FileFormat = 51)    #FileFormat = 51 is for .xlsx extension
wb.Close()                               #FileFormat = 56 is for .xls extension
excel.Application.Quit()

Just wrapped the code above in a function together with better path handling to make sure the excel process is getting closed.

from pathlib import Path
import win32com.client as win32
    
def convert_xls_to_xlsx(path: Path) -> None:
    excel = win32.gencache.EnsureDispatch('Excel.Application')
    wb = excel.Workbooks.Open(path.absolute())

    # FileFormat=51 is for .xlsx extension
    wb.SaveAs(str(path.absolute().with_suffix(".xlsx")), FileFormat=51)
    wb.Close()
    excel.Application.Quit()