Anyone happen to have optimization hints for this loop?

[dp_pearce]

Thank you so much for all your advice. I have learnt a lot.

In the end, the solution was perhaps self evident. Why try and build a
huge string AND THEN write it to file when you can just write it to
file? Writing this much data directly to file completed in ~1.5
seconds instead of the 3-4 seconds that any of the .join methods
produced.

Interestingly, I found that my tests agreed with Bruno. There wasn't a
huge change in speed between a lot of the other methods, other than
them looking a lot tidier.

Again, many thanks.

Dan