DerivVar instance has no attribute '__float__'

[Lee Harr]

I just installed the Scientific module and am trying it out:

>>> from Scientific.Functions.Derivatives import DerivVar
>>> from math import sin
>>> print sin(DerivVar(2))
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
AttributeError: DerivVar instance has no attribute '__float__'
>>> 


I googled for DerivVar float and found a message from one
person last year with the same problem, but no posted solution.

I am using:
Python 2.2
FreeBSD 4.5
py22-numeric-20.3
py22-scientific-2.2

Anyone have a hint?