intspan is a set subclass that conveniently stores sets of integers. Sets can be created from and displayed as integer spans such as 1-3,14,29,92-97 rather than exhaustive member listings. Compare:

[1, 2, 3, 14, 29, 92, 93, 94, 95, 96, 97]

While they indicate the same values, the intspan is more compact. Even more important, it better divulges the contiguous nature of parts of the collection. It is easier for humans to quickly determine the “shape” of the collection and ascertain “what’s missing?”

When iterating, pop()-ing an item, or converting to a list, intspan behaves as if it were an ordered–in fact, sorted–collection. A key implication is that, regardless of the order in which items are added, an intspan will always be rendered in the most compact, organized form possible.

The main draw is having a convenient way to specify (possibly discontinuous) ranges–for example, rows to process in a spreadsheet. It can also help you quickly identify or report which items were not successfully processed in a large dataset.