We saw the zip() function in Chapter 4, Working with Collections. The zip_longest() function differs from the zip() function in an important way: whereas the zip() function stops at the end of the shortest iterable, the zip_longest() function pads short iterables and stops at the end of the longest iterable.

The fillvalue keyword parameter allows filling with a value other than the default value, None.

For most exploratory data analysis applications, padding with a default value is statistically difficult to justify. The Python Standard Library document shows a few clever things that can be done with the zip_longest() function. It's difficult to expand on these without drifting far from our focus on data analysis.