floating point in python gives a wrong answer

Question

I calculated the following:

>>> float(10.0-9.2)
0.800000000000000*7*

even doing 10.0-9.2 gave the above result. Why is the extra 7 coming in the result?

I'm on python 3.2.

Answer 1

Floating point arithmetic has built-in problems as it's based on a binary approximation of numbers.

There is a good explanation of this in the Python docs.

You can check out the decimal module if you need more exact answers.

Answer 2

You can use round()

for example:

print(round(10 - 9.2, 2))