On 2014-04-15 19:18, Phil Dobbin wrote: > I'm confused as to this part: > > '>>> 0.1 + 0.1 + 0.1 - 0.3 > 5.55111.....' > > What I'm wondering is why the first calculation that arrives at > '5.55111...' is so far out?
You omit one key detail in your "....", the "e-17" which means that is 5.55111... times 10^-17 which is a REALLY small number. To better show that, have it formatted to place: >>> "%55.55f" % (0.1 + 0.1 + 0.1 - 0.3) '0.0000000000000000555111512312578270211815834045410156250' For most engineering purposes, that's effectively zero. It comes about because of how floating-point numbers are represented internally. You can read a lot more than anybody should want to know at [1]. By using the Decimal module, you remove some of that imprecision. -tkc [1] http://en.wikipedia.org/wiki/Ieee_float -- https://mail.python.org/mailman/listinfo/python-list
