10/3.14159265=3.18309886548 it is meant that you just cut answer up to the 4 digits after decimal point. So 10/3.14159265=3.1830 up to the 4 digits after decimal point. By the way, according to the reference http://docs.python.org/library/functions.html#round (read note) you can not always trust the results of round() function approximation for floats.