Incremented floats are not equal to each other

Possible duplicate:
Why decimal numbers cannot be represented exactly in binary format?
The program is not included in the if statement

So, I'm trying to run a program with two variables, when one variable is equal to the other, it performs a function. In this case, print spam. However, for some reason, when I run this program, I do not get any result, although I know that they are equal.

g=0.0
b=3.0

while g < 30.0:
    if g==b:
        print "Hi"
    g+=.1
    print g, b