AttributeError in ScientificPython, why?

[Daniel Reuter]

Reply-To: 
Hello there,

I recently installed ScientificPython, hope that someone on this list has
some experiences with it.
Now if I enter the following in interactive mode:

import Scientific.Functions.Derivatives
import math
from Scientific.Functions.Derivatives import DerivVar
print math.sin(DerivVar(2))

I should, due to the manual get something like this:
(0.909297426826, [-0.416146836547])

However, I get this:
Traceback (innermost last):
  File "<stdin>", line 1, in ?
AttributeError: __float__

I'm quite new to python and the library reference doesn't tell that much
about the AttributeError exception, so it would be nice, if someone could
enlighten me a bit, something wrong with my imports perhaps?
TIA,
Regards,
Daniel