To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？

[iMath]

To get the accurate value of 1 - 0.999999999999999 ,how to implement the python 
algorithm ？
BTW ，Windows’s calculator get the accurate value ，anyone who knows how to 
implement it ?
-- 
http://mail.python.org/mailman/listinfo/python-list