x = 10.0
for i in range(10):
x +=0.1
print x == 11.0

Why is this false? I print x and it equals 11.0

Question

x = 10.0
for i in range(10):
        x +=0.1
print x == 11.0

Why is this false?  I print x and it equals 11.0

rsmith6559 · Answer

Floating point is basically a binary scientific notation.  It's accuracy is greatest when dealing with numbers that are close to a power of 2.  A number like 11.0, although it prints as 11.0, is probably  several ten thousandths off.  That's enough so that it doesn't compare equal to your literal 11.0.

anonymous · Answer

At the point in the lecture series where I'm at, the prof alludes to a future lecture that discusses the internal representation of reals ie floating point.  I'm guessing that if there's a function that can specify that the real number be accurate to the nearest tenth then I imagine this code snippet could work.

anonymous · Answer

I found this technical explanation http://docs.python.org/2/tutorial/floatingpoint.html#tut-fp-issues

anonymous · Answer

Thank you for  the answer.  I thought that was the reason for this output.  Didn't expect it on a practice quiz.