This is a very fast factorization algorithm. I've concocted it from several sources. It would be hard to find one faster than this.

python_factorization.py

from math import sqrt

"""
	Fast factorization algorithm. Uses tuples instead of lists  
	and sqrt over exponentiation.
"""
def factors(n):
    return set(x for tup in ([i, n//i] 
                for i in range(1, int(sqrt(n))+1) if n % i == 0) for x in tup)