All explained here: https://www.python.org/dev/peps/pep-0324/ https://www.python.org/dev/peps/pep-0324/ tl;dr * Security (including avoiding holes like shells

All explained here: https://www.python.org/dev/peps/pep-0324/ https://www.python.org/dev/peps/pep-0324/ tl;dr * Security (including avoiding holes like shellshock) * Unification of process handling under one core library. * Easier detection of errors in processes. * Easier control of stderr/stdout. * Universal newline support. * Elimination of race conditions with .communicate()