Hi List, I have to sum up an unknown number of ndarrays of the same size. These arrays, possibly thousands in number, are provided by an iterator. Right now I use python reduce with operator.add. Does that invoke the corresponding ufunc internally, I want to avoid creating temporaries. With ufunc I know how to do it, but not sure how to make use of that in reduce. It is not essential that I use reduce though, so I would welcome idiomatic and efficient way of executing this. So far I have stayed away from building an ndarray object and summing across the relevant dimension. Is that what I should be doing ? Different invocations of this function has different number of arrays, so I cannot pre-compile away this into a numexpr. Thanks and regards srean