gistfile1.py

>>> import math
>>> def length(v):
...   return math.sqrt(sum(term * term for term in v))
... 
>>> def dot(v1, v2):
...   return sum(term1 * term2 for (term1, term2) in zip(v1, v2))
... 
>>> def vcos(v1, v2):
...   return dot(v1, v2) / (length(v1) * length(v2))
... 

>>> vcos((1, 0, 0), (0, 1, 0))
0.0

>>> vcos((1, 0, 0), (0, 5, 0))
0.0

>>> vcos((50, 1, 0), (0, 5, 0))
0.01999600119960014

>>> vcos((1, 50, 0), (0, 5, 0))
0.9998000599800071

>>> vcos((1, 5000000, 2), (0, 1, 0))
0.9999999999999