experiment i'd like to understand why the new one is only barely as fast as the old one

output.log

roundrobin 0.148742198944
roundrobin_stable 0.169327974319
roundrobin_rotate 0.246076822281
roundrobin
         204064 function calls in 1.340 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
     2000    0.000    0.000    0.000    0.000 :0(iter)
       20    0.000    0.000    0.000    0.000 :0(len)
   101000    0.320    0.000    0.320    0.000 :0(next)
        1    0.000    0.000    0.000    0.000 :0(range)
        1    0.008    0.008    0.008    0.008 :0(setprofile)
     2020    0.008    0.000    0.008    0.000 itertool_example.py:10(<genexpr>)
    99020    0.664    0.000    0.992    0.000 itertool_example.py:6(roundrobin)
        1    0.340    0.340    1.332    1.332 itertool_example.py:70(loop)
        1    0.000    0.000    1.340    1.340 profile:0(<function loop at 0x2776488>)
        0    0.000             0.000          profile:0(profiler)


roundrobin_stable
         404044 function calls in 2.532 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
    99000    0.312    0.000    0.312    0.000 :0(append)
     2000    0.012    0.000    0.012    0.000 :0(iter)
   101000    0.300    0.000    0.300    0.000 :0(next)
   101000    0.340    0.000    0.340    0.000 :0(popleft)
        1    0.000    0.000    0.000    0.000 :0(range)
        1    0.000    0.000    0.000    0.000 :0(setprofile)
    99020    1.272    0.000    2.244    0.000 itertool_example.py:21(roundrobin_stable)
     2020    0.008    0.000    0.020    0.000 itertool_example.py:23(<genexpr>)
        1    0.288    0.288    2.532    2.532 itertool_example.py:70(loop)
        1    0.000    0.000    2.532    2.532 profile:0(<function loop at 0x2776488>)
        0    0.000             0.000          profile:0(profiler)


roundrobin_rotate
         305044 function calls in 1.840 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
     2000    0.004    0.000    0.004    0.000 :0(iter)
   101000    0.292    0.000    0.292    0.000 :0(next)
     2000    0.008    0.000    0.008    0.000 :0(popleft)
        1    0.000    0.000    0.000    0.000 :0(range)
    99000    0.304    0.000    0.304    0.000 :0(rotate)
        1    0.000    0.000    0.000    0.000 :0(setprofile)
    99020    0.936    0.000    1.560    0.000 itertool_example.py:36(roundrobin_rotate)
     2020    0.016    0.000    0.020    0.000 itertool_example.py:38(<genexpr>)
        1    0.280    0.280    1.840    1.840 itertool_example.py:70(loop)
        1    0.000    0.000    1.840    1.840 profile:0(<function loop at 0x2776488>)
        0    0.000             0.000          profile:0(profiler)

roundrobin.py

from __future__ import print_function
from collections import deque
from itertools import cycle, islice
import pytest

def roundrobin(*iterables):
    " >> roundrobin('ABC', 'D', 'EF') --> A D E B F C"
    # Recipe credited to George Sakkis
    pending = len(iterables)
    iters = cycle(iter(it) for it in iterables)
    while pending:
        try:
            for item in iters:
                yield next(item)
        except StopIteration:
            pending -= 1
            iters = cycle(islice(iters, pending))



def roundrobin_stable(*iterables):
    " >> roundrobin('ABC', 'D', 'EF') --> A D E B F C"
    items = deque(iter(x) for x in iterables)
    pop = items.popleft
    push = items.append
    while items:
        item = pop()
        try:
            yield next(item)
        except StopIteration:
            pass
        else:
            push(item)


def roundrobin_rotate(*iterables):
    " >> roundrobin('ABC', 'D', 'EF') --> A D E B F C"
    items = deque(iter(x) for x in iterables)
    while items:
        try:
            yield next(items[0])
        except StopIteration:
            items.popleft()
        else:
            items.rotate(-1)

funcs = [roundrobin, roundrobin_stable, roundrobin_rotate]

@pytest.mark.parametrize('func', funcs)
def test_func(func):
    assert ''.join(func('ABC', 'D', 'EF')) == 'ADEBFC'



def time_it(number=100):
    import timeit
    setup = (
        'import random;'
        'params = [range(x) for x in range(100)];'
        'random.shuffle(params);'
        'from __main__ import {name} as func'
    )
    stmt = 'list(func(*params))'
    for func in funcs:
        print(func.__name__, timeit.Timer(
            setup=setup.format(name=func.__name__),
            stmt=stmt).timeit(number=number))


def loop(func, params):
    for i in range(20):
        list(func(*params))


def profile_it():
    params = [range(x) for x in range(100)];
    import profile
    for func in funcs:
        print(func.__name__)
        profiler = profile.Profile()
        profiler.runcall(loop, func, params)
        profiler.print_stats()

if __name__ == '__main__':
    time_it()
    profile_it()