We know that 0.1 + 0.1 + 0.1 - 0.3 = 0.0
But in python 0.1 + 0.1 + 0.1 - 0.3 = 5.5511151231257827e-017

Is there any way I can get 0.0...??

Well a simple fix would be to multiply everything by 10. Ie:

import os
print float(1+1+1-3)/10
os.system("pause")

To be at sure side add in beginning of your numeric Python 2 code:

from __future__ import division

This makes 1/4 produce 0.25, not 0 (integer division). For integer division use // operator.

Thank you very much everyone... Now i understand the reason behind it... Thank you!