gp.py is a thin subprocess wrapper around a gnuplot instance.  There are convenience methods for gnuplot 'set', 'unset', 'plot', and 'splot' commands.  It is trivial to add more of these if needed.  Otherwise the gnuplot interaction is as plain as conveniently possible.  Data can be passed to gnuplot by temporary files or gnuplot here documents (for >=gnuplot-4.7.p0).  Other than this, there is no 'magic': no obfuscation of gnuplot syntax or commands.

All other python gnuplot wrappers I've seen try to infiltrate lots of specialized code to assist specific gnuplot use cases needed or imagined by the author.  I have always found this to be cumbersome and to further confuse gnuplot's already intricate syntax.  Gnuplot is so old and big that the work necessary to implement a python interface layer in order to satisfy everyone's python-wrapped gnuplot use cases is far too much more effort than I--and it appears anyone else who has written a gnuplot wrapper--am willing to make.