floating point - Python Decimal Module - Undesired Float-Like Output? -

this imagine extremely simple - why in following 2 values y not == 0? thought whole point of decimal module rid of float dust ...the following extremely simplified version of mathematical routine passes numbers around variables.

from decimal import *  getcontext().prec = 2  q = decimal(0.01)  x = decimal(0.10) * decimal(0.10)  y = decimal(x) - decimal(q)  print(x,y, decimal(y))  ''' x== 0.010  y== -2.1e-19  decimal(y) == -2.1e-19 ''' 

try specifying numbers strings

>>> decimal('0.10') * decimal('0.10') - decimal('0.0100') >>> decimal('0.000')