Your best bet is probably to look into your LISP environment's FFI (Foreign Function Interface). Most LISP environments have some way to call C code directly. Insofar as going back the other way... that I'm a little more sketchy on. Guile (the Scheme compiler from GNU) is a strong contender, though. It's not Common LISP, but it's a LISP with copious documentation for how to call it from C.
I really can't see a reason to use Python as a glue layer. I'd recommend rewriting your LISP code in Python before I'd recommend using Python to interface between Common LISP and C. -- http://mail.python.org/mailman/listinfo/python-list
