This is actually expected because that is just how floating point works in programming (see http://en.wikipedia.org/wiki/Floating_point for all the gnarly details).

If you want exact decimal arithmetic, use the decimal module (which got significantly faster in Python 3.3)::

>>> import decimal
>>> decimal.Decimal('.3') - decimal.Decimal('.1')
Decimal('0.2')
>>> decimal.Decimal('.05') + decimal.Decimal('.01')
Decimal('0.06')