On Wednesday I started looking into py-orbit (the orbit tracking code for python). In order to quickly see what happens with the particles I wanted to be able to directly access the particle coordinates as a numpy array. The builtin c functions will only give you a pointer to the particle array and the builtin python functions give single particle coordinates. Accessing those for turn-by-turn diagnostics would give you a huge overhead of python code. This is not a flaw as everything time-critical in py-orbit is written on the C++ level. Nevertheless as a beginner and cython/python lover I would like to be able to use numpy for a fast view on the particle coordinates. For the direct access on a c array pointer via numpy I found help on a gist by Gael Varoquaux.
Unfortunately it turns out that py-orbit allocates memory in chunks of 10 particles. So the two dimensional array of particles is not a continuous chunk of memory and therefore there is, as I see it no easy way to access it as a numpy array. Nevertheless I think it is worthwhile to post this here so others do not waste time of this.
If you want it really badly I think the way to go is to modify py-orbit to allocate the memory for all particles at once in the beginning, but instead you can also just access the arrays in cython directly so I decided it was not worth the effort.