pl/python requires pthreads in order to work.  OpenBSD does not allow
shared objects that link to pthreads to be opened via dlopen if the
executable program does not link to pthreads.  So to use pl/python, you
must ensure that PostgreSQL links to libpthread.  The easiest way to do
this is adding the following login class to login.conf:

postgresql:\
        :setenv=LD_PRELOAD=libpthread.so:\
        :tc=daemon: 
