numpy array access
I would be very cautious about over-riding the [] operator through the __getitem__() method. Although it will be fine with your own code, I can easily imagine that when the array gets passed to an arbitrary library function, you could get problems. 
For example, if the function explicitly tried to get all values in the array as A[0:-1], it would maps to A[offset:offset-1], which will be an empty array for any positive or negative value of offset. This may be a little contrived, but it illustrates the general problem.
Therefore, I would suggest that you create a wrapper function for your own use (as a member function may be most convenient), but don't muck around with __getitem__().
I need to create a numpy array of N elements, but I want to access the
array with an offset Noff, i.e. the first element should be at Noff and
not at 0. In C this is simple to do with some simple pointer arithmetic, i.e.
I malloc the array and then define a pointer and shift it appropriately.
Furthermore, I do not want to allocate N+Noff elements, but only N elements.
Now for numpy there are many methods that come to my mind:
(1) define a wrapper function to access the array
(2) overwrite the [] operator
(3) etc
But what is the fastest method to realize this?
Thanks a lot!
Mark