Here's a patch that looks likes Victor's from the duplicate, but with tuples covered as well. I ran some straight forward micro benchmarks but haven't bothered running the benchmark suite yet. Unsurprisingly, optimized paths are faster, and the others take a penalty.

[0]byrnez@byrnez-laptop:~/git/python$ ./python.orig -m timeit -s "l = [1,2,3,4,5,6]" "l[3]"
10000000 loops, best of 3: 0.0306 usec per loop
[0]byrnez@byrnez-laptop:~/git/python$ ./python -m timeit -s "l = [1,2,3,4,5,6]" "l[3]"
10000000 loops, best of 3: 0.0243 usec per loop

[0]byrnez@byrnez-laptop:~/git/python$ ./python.orig -m timeit -s "l = (1,2,3,4,5,6)" "l[3]"
10000000 loops, best of 3: 0.0291 usec per loop
[0]byrnez@byrnez-laptop:~/git/python$ ./python -m timeit -s "l = (1,2,3,4,5,6)" "l[3]"
10000000 loops, best of 3: 0.0241 usec per loop

[0]byrnez@byrnez-laptop:~/git/python$ ./python.orig -m timeit -s "l = 'asdfasdf'" "l[3]"
10000000 loops, best of 3: 0.034 usec per loop
[0]byrnez@byrnez-laptop:~/git/python$ ./python -m timeit -s "l = 'asdfasdf'" "l[3]"
10000000 loops, best of 3: 0.0366 usec per loop

[0]byrnez@byrnez-laptop:~/git/python$ ./python.orig -m timeit -s "l = [1,2,3,4,5,6]" "l[:3]"
10000000 loops, best of 3: 0.124 usec per loop
[0]byrnez@byrnez-laptop:~/git/python$ ./python -m timeit -s "l = [1,2,3,4,5,6]" "l[:3]"
10000000 loops, best of 3: 0.125 usec per loop