PyEphem Under The Hood - How Does It Calculate Position Of Planets?

In space SE it was suggested I use PyEphem to calculate orbits from two-line elements. Now I'm curious how it calculates 'build-in' solar system objects like the planets and their

Solution 1:

According to the PyEphem Readme

The underlying numeric routines are coded in C and are the same ones that drive the popular XEphem astronomy application, whose author, Elwood Charles Downey, generously gave permission for their use in PyEphem.

The C library is called libastro. Inspection of the libastro source reveals that it is in fact using VSOP 87.