Python built-in sum function vs. for loop performance

Question

I noticed that Python\'s built-in sum function is roughly 3x faster than a for loop when summing a list of 1 000 000 integers:

import timeit

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Answer 1

However if the loop is just adding 1 each iteration starting from 0 you could use the fast trick addition. The sum output should be 499999500000 for range(1000000)

import timeit

def sum1():
    s = 0
    for i in range(1000000):
        s += i
    #print s    
    return s

def sum2():

    return sum(range(1000000))

def sum3():
    s = range(1000000)
    s = ((s[1]+s[-1])/2) * (len(s)-1)
    #print(s)
    return s

print 'For Loop Sum:', timeit.timeit(sum1, number=10)
print 'Built-in Sum:', timeit.timeit(sum2, number=10)
print 'Fast Sum:', timeit.timeit(sum3, number=10)

#prints
#For Loop Sum: 1.8420711
#Built-in Sum: 1.1081646
#Fast Sum: 0.3191561