I mean, whenever I have this problem, I fall back on my (terrible) SPSS habits and just recode NaN to -999. With integer datasets that mostly works fine. You could come up with some alternative solution, too.
Personally, I'm an amateur at best, but Pandas has made it possible for me to do some really handy things.
Personal favorite feature: multindexing on rows AND Columns. Multiindex is such a common pattern, and so poorly handled in things like excel. Pandas really saves a lot of time with re-indexing, pivoting, stacking, or transposing data with multi indexes.
Personally, I'm an amateur at best, but Pandas has made it possible for me to do some really handy things.
Personal favorite feature: multindexing on rows AND Columns. Multiindex is such a common pattern, and so poorly handled in things like excel. Pandas really saves a lot of time with re-indexing, pivoting, stacking, or transposing data with multi indexes.