It used to be that the best way to compare floating point numbers while disregarding the inherent epsilon was to use `str(x) == str(y)`. It looks like that workaround doesn't work anymore in 3.4.
What's the recommended way to do this now? >>> format(.01 + .01 + .01 + .01 + .01 + .01, 'g') == format(.06, 'g') True On Saturday, June 21, 2014 12:24:24 PM UTC-7, Ned Deily wrote: > In article > > <captjjmrkpd5k__h9qg12q+arafzvan6egudtmedge2ccaqe...@mail.gmail.com>, > > Chris Angelico <ros...@gmail.com> wrote: > > > Also, when you're looking at how things print out, consider looking at > > > two things: the str() and the repr(). Sometimes just "print(p)" > > > doesn't give you all the info, so you might instead want to write your > > > loop thus: > > > > > > z = 0.01 > > > p = 0.0 > > > for i in range(19): > > > p += z > > > print(str(p) + " -- " + repr(p)) > > > Sometimes you can get extra clues that way, although in this instance > > > I think you won't. > > > > Actually, I think this is one case where you would get extra clues (or > > extra headscratching) if you run the code with various releases of > > Python. > > > > $ python2.6 b.py > > 0.01 -- 0.01 > > 0.02 -- 0.02 > > 0.03 -- 0.029999999999999999 > > 0.04 -- 0.040000000000000001 > > 0.05 -- 0.050000000000000003 > > 0.06 -- 0.060000000000000005 > > 0.07 -- 0.070000000000000007 > > 0.08 -- 0.080000000000000002 > > 0.09 -- 0.089999999999999997 > > 0.1 -- 0.099999999999999992 > > 0.11 -- 0.10999999999999999 > > 0.12 -- 0.11999999999999998 > > 0.13 -- 0.12999999999999998 > > 0.14 -- 0.13999999999999999 > > 0.15 -- 0.14999999999999999 > > 0.16 -- 0.16 > > 0.17 -- 0.17000000000000001 > > 0.18 -- 0.18000000000000002 > > 0.19 -- 0.19000000000000003 > > > > $ python2.7 b.py > > 0.01 -- 0.01 > > 0.02 -- 0.02 > > 0.03 -- 0.03 > > 0.04 -- 0.04 > > 0.05 -- 0.05 > > 0.06 -- 0.060000000000000005 > > 0.07 -- 0.07 > > 0.08 -- 0.08 > > 0.09 -- 0.09 > > 0.1 -- 0.09999999999999999 > > 0.11 -- 0.10999999999999999 > > 0.12 -- 0.11999999999999998 > > 0.13 -- 0.12999999999999998 > > 0.14 -- 0.13999999999999999 > > 0.15 -- 0.15 > > 0.16 -- 0.16 > > 0.17 -- 0.17 > > 0.18 -- 0.18000000000000002 > > 0.19 -- 0.19000000000000003 > > > > $ python3.4 b.py > > 0.01 -- 0.01 > > 0.02 -- 0.02 > > 0.03 -- 0.03 > > 0.04 -- 0.04 > > 0.05 -- 0.05 > > 0.060000000000000005 -- 0.060000000000000005 > > 0.07 -- 0.07 > > 0.08 -- 0.08 > > 0.09 -- 0.09 > > 0.09999999999999999 -- 0.09999999999999999 > > 0.10999999999999999 -- 0.10999999999999999 > > 0.11999999999999998 -- 0.11999999999999998 > > 0.12999999999999998 -- 0.12999999999999998 > > 0.13999999999999999 -- 0.13999999999999999 > > 0.15 -- 0.15 > > 0.16 -- 0.16 > > 0.17 -- 0.17 > > 0.18000000000000002 -- 0.18000000000000002 > > 0.19000000000000003 -- 0.19000000000000003 > > > > What's going on here is that in Python 2.7 the repr() of floats was > > changed to use the minimum number of digits to accurately roundtrip the > > number under correct rounding. For compatibility reasons, the str() > > representation was not changed for 2.7. But in Python 3.2, str() was > > changed to be identical to repr() for floats. It's important to keep in > > mind that the actual binary values stored in float objects are the same > > across all of these releases; only the representation of them as decimal > > characters varies. > > > > https://docs.python.org/2.7/whatsnew/2.7.html#other-language-changes > > > > http://bugs.python.org/issue9337 > > > > -- > > Ned Deily, > > n...@acm.org -- https://mail.python.org/mailman/listinfo/python-list
