refactor!: replace os.listdir() with os.scandir() In many places we did a listdir() then a stat to see if it's a file or directory. This change removes the need for the stat call. Also for larger directories, scandir() is an iterator, so less memory use. There is one remnant of listdir used in an error handler. That requires a stat on each element in the directory, so there is no benefit to using scandir() other than a slight memory saving on a rarely used piece of code. BREAKING CHANGE: Python 2 requires installation of scandir pip package after this commit.