shouldn't this raise an exception?

[casevh]

>>> from decimal import *
>>> getcontext()
Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[InvalidOperation, DivisionByZero, Overflow])
>>> Decimal('1E-999999')*Decimal('1E-99')
Decimal('0E-1000026')
>>> getcontext()
Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[Clamped, Inexact, Rounded, Subnormal, Underflow], traps=[InvalidOperation, DivisionByZero, Overflow])
>>> 

Compare the differences in the output of getcontext() before and after operation that generates the underflow. flags now has a list of the special conditions. The Underflow flag was set. traps is a list of the flags, that when set, raise an exception. You can add Underflow to the traps if you want to raise an exception.

>>> setcontext(DefaultContext)
>>> getcontext()
Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[InvalidOperation, DivisionByZero, Overflow])
>>> getcontext().traps[Underflow] = True
>>> getcontext()
Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[InvalidOperation, DivisionByZero, Overflow, Underflow])
>>> Decimal('1E-999999')*Decimal('1E-99')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
decimal.Underflow: [<class 'decimal.Underflow'>]
>>>