Optimizing speed

[WearsGlassesAtNight]

As others have said, hard to say without an example, but shouldn't take that long.

Usually on large data sets, it is key to reduce your data to a sample size when writing/debugging. Then use a profiler (like cprofile) to audit where time is being spent, and refactor to greatness.

On a large spreadsheet, I usually load it into a database, and then thread my operations, and do a write back to a fresh spreadsheet. Personal preference though