Python 2.6 set() vs locals()['_[1]']

gistfile1.txt

Python 2.6.9 |Continuum Analytics, Inc.| (unknown, Jan 10 2014, 13:33:57) 
[GCC 4.2.1 (Apple Inc. build 5577)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import timeit
>>> from math import sqrt
>>> 
>>> n = 100
>>> sqrt_n = int(sqrt(n))
>>> 
>>> def with_set():
...     primes = [j for i in range(2,sqrt_n) for j in range(i*2, n, i)]
...     return set(primes)
... 
>>> def with_locals():
...     return [j for i in range(2,sqrt_n) for j in range(i*2, n, i) 
...             if j not in locals()['_[1]']]
... 
>>> timeit.timeit(with_set, number=100000)
1.5858581066131592
>>> timeit.timeit(with_locals, number=100000)
13.023312091827393