Benchmark: timing 100 iterations of with_chdir, without_chdir...
with_chdir: 25 wallclock secs ( 3.02 usr + 20.31 sys = 23.33 CPU) @  4.29/s (n=100)
without_chdir: 28 wallclock secs ( 3.76 usr + 21.65 sys = 25.41 CPU) @  3.94/s (n=100)