'sla' is a limited Python extension or slalib-related stuff.

Installation is the usual:

python setup.py install --prefix=my_installation_directory

but you need to have installed the SLALIB C library first and defined
an environment variable TRM_SOFTWARE to point to the directory containing
lib and include which contain the libraries and include files.

Documentation available from 'pydoc trm.sla' once you have installed
the software.

Tom Marsh