In my experience edanm is correct. map/reduce/filter are faster with built-in functions, but list comprehensions are faster with user-defined ones

For eg. using python 2.5.2

In [9]: l = ['10'] * 5000000

In [10]: timeit -n5 map(int, l)

5 loops, best of 3: 1.29 s per loop

In [11]: timeit -n5 [int(i) for i in l]

5 loops, best of 3: 1.64 s per loop