I have an excel file with more than 600,000 rows. I need to clean up names in the cell so I called the file as read_only and revise the name with the RE module. Then I open another file as write_only and append the revised names to it. The first 5,000 cells are done fast but it seems that after it maxed out its memory, the computer literally reads the original cell one by one, changes it, and saves it one by one. Each row takes one second. (I had the row number printed in the loop) At this rate, The computer will finish the job in about a week. It would be great if I could get the job done faster.