需要说明为什么以下代码跨越无穷大

Question

I am a beginner to python and was wondering why the code spans for infinity when it should've been stopped at 1.

def main():
    i = 0.0
    while i != 1.0:
        print("i =", i)
        i += 0.1
main()

Answer 1

This is a well known problem in Python.

Your variable i never becomes exactly 1, but instead becomes 0.9999999999999999.

Do instead:

def main():
    i = 0.0
    while i <= 1.0:
        print("i =", i)
        i += 0.1

Answer 2

In the general case, of course you shouldn't compare floats by equality, but there's more to it: when you're adding like this you get floating point accumulation error.

You can use an integer counter instead and apply multiplication every time to avoid that.

def main():
    i = 0.0
    count = 0
    while i < 1.0:
        print("i =", i)
        count += 1
        i = count*0.1

main()

I have replaced i != 1.0 by i < 1.0 because that's all you need, but it even works with != (although I don't recommend that) now because there's no accumulation error anymore the way it's computed with the integer counter.