It says:

> os.utimensat(dirfd, path[, atime=(atime_sec, atime_nsec), mtime=(mtime_sec, mtime_nsec), flags=0])
> Updates the timestamps of a file with nanosecond precision. The atime and mtime tuples default to None, which sets those values to the current time.

It should be the other way around: atime=None, mtime=None in the signature and explain in the body how they look like. It looks like atime_sec and atime_nsec are some magic constants this way.