As RCGothic said, lookup+interpolation is one of the faster results.
Some of the CPU specific assembly calls for sincos uses lookup tables.
IMO, I'm unsure if a python dictionary is the best choice for this.
Floating point issues could arise from the use of it. I mean, the look up could fail over this.
If you are going to do use degree's as the basis, then a d%360 lookup to a list (the [] variant, it seems more optimised for lookups) could be even faster.
Also, this is very interresting:
http://www.devmaster.net/forums/showthread.php?t=5784Atleast, for C/C++, but it might also be applicable for Python, it doesn't beat speed for lookup (assuming you do integer lookups), but it's faster than a direct call to sincos and more accurate than a look up (I think).