>>> import spam, numpy
>>> a = spam.vector3d()
>>> a[0]=1
>>> a[1]=1
>>> a[2]=1
>>> b = numpy.array([1.2,2.3,4.5])
>>> c = a+b
>>> c
array([ 2.2,  3.3,  5.5])
>>> a+=a
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +=: 'spam.vector3d' and 'spam.vector3d'
>>>