Hello, I've been working on a little project lately centered around distance metrics ( https://github.com/jakevdp/pyDistances ). The idea was to create a set of cython distance metrics that can be called as normal from python with numpy arrays, but which also expose low-level C function pointers so that the same metrics can be called directly on memory buffers from within cythonized tree-based KNN searches (KD Tree, Ball Tree, etc.), without any python overhead. I initially had in mind developing this for scikit-learn in order to extend the capability of Ball Tree, but it occurred to me that this might be nice to have in scipy as well. The speed of computing a distance matrix is comparable to that of pdist/cdist in scipy.spatial.distance (a few metrics are slightly faster, a few are slightly slower). The primary advantage to this approach is the exposure of underlying C functions which can be easily imported and called from other cython scripts. I think there are several other advantages over the current scipy implementation. Because the new code is pure cython, it would likely be easier to maintain and to add metrics than the current scipy setup, which relies on C routines wrapped by-hand using the numpy C-API. Because all distance functions rely on the same set of underlying cython routines, there are fewer places for error (for instance, currently the scipy.spatial.distance boolean routines return different results depending on whether you call the metrics directly or use cdist/pdist) I'm curious what people think: could a framework like this replace the current scipy.spatial.distances implementation? Are there any disadvantages that I'm not noticing? Thanks Jake