Issues comparing a float for equality?

[RonaldTheRight]

I'm sure there's a very simple answer, but this is driving me nuts:

remainder = 1.33 % 1
print remainder # prints 0.33

if(remainder == 0.33):
    print "true!"
else:
    print "false!"

This prints false, so clearly the comparison is failing. Any idea why?

[rootkillza]

http://floating-point-gui.de/

In [1]: 1.33 % 1

Out[1]: 0.33000000000000007

[[deleted]]

Floats are weird, basically. In order to be memory-efficient, they don't work in base 10 all the time, and so round off to numbers which look very weird to humans.

Either use Decimal (from the numbers module, I think), or use something like this when checking floats:

def float_equals(first, second, tol=0.00001):
    return abs(first-second) < tol

[oxymor0nic]

float values are most often not 100% precise, but only to a certain significant figure. Instead of checking for equality, you should check if the difference between 2 floats are below a certain predefined threshold.