Performing Accurate Decimal Operations

In python the decimal calculations using the IEEE 754 algorithm.
>>> a = 4.1
>>> b = 2.2
>>> a + b
6.300000000000001

that means that
>>> (a + b) == 6.3 
False
Because python's float type stores data using the native representations.

If you want more accuracy Decimal class from decimal module can help you with that.

>>> from decimal import Decimal
>>> a = Decimal('4.1')
>>> b = Decimal('2.2')
>>> a + b
Decimal('6.3')
>>> (a + b) == Decimal('6.3')
True