Ray/sphere intersection in Python

rs_intersect.py

#!/usr/bin/env python
import timeit

def dot(a, b):
	"""Dot product"""
	return a[0]*b[0] + a[1]*b[1] + a[2]*b[2]

def rs_intersect(R0, d, C, r):
	"""Ray/sphere intersection"""
	R0 = (R0[0] - C[0], R0[1] - C[1], R0[2] - C[2])
	dDotR0 = dot(d, R0)
	t = -dDotR0 - (dDotR0*dDotR0 - dot(R0, R0) + r*r)**0.5
	return (R0[0] + t*d[0], R0[1] + t*d[1], R0[2] + t*d[2])

R0 = (0, 0, -10)
d = (0.01/1.002, 0.01/1.002, 1/1.002)
C = (0, 0, 0)
r = 1
def test():
	global R0, d, C, r
	rs_intersect(R0, d, C, r)

print timeit.timeit('test()', setup='from __main__ import test; gc.enable()', number=1000000)