def original(iterable, n=None):
    iterable = tuple(iterable)
    if not iterable:
        return iter(())
    counter = count() if n is None else range(n)
    return ((i, item) for i in counter for item in iterable)


def zip_chain(iterable, n=None):
    seq = tuple(iterable)
    if not seq:
        return iter(())
    counter = count() if n is None else range(n)
    return zip(
        chain.from_iterable(map(repeat, counter, repeat(len(seq)))),
        cycle(seq)
    )


def chain_zip(iterable, n=None):
    seq = tuple(iterable)
    if not seq:
        return iter(())
    counter = count() if n is None else range(n)
    return chain.from_iterable(
        map(zip, map(repeat, counter), repeat(seq))
    )


def chain_ziplongest(iterable, n=None):
    seq = tuple(iterable)
    if not seq:
        return iter(())
    counter = count() if n is None else range(n)
    return chain.from_iterable(
        zip_longest((), seq, fillvalue=i)
        for i in counter
    )


funcs = [
    original, 
    zip_chain,
    chain_zip,
    chain_ziplongest,
]


from itertools import *
from collections import deque
from timeit import timeit
from statistics import mean, stdev
import sys
import random

# Correctness
for f in funcs:
    print(*f('AB', 3))

# Speed
consume = deque(maxlen=0).extend
args = 'range(1000), 3'
args = 'range(3), 1000'
times = {f: [] for f in funcs}
def stats(f):
    ts = [t * 1e6 for t in sorted(times[f])[:5]]
    return f'{mean(ts):5.1f} ± {stdev(ts):3.1f} μs '
for _ in range(100):
    for f in random.sample(funcs, len(funcs)):
        t = timeit(f'consume(count_cycle({args}))', 'from __main__ import f as count_cycle, consume', number=10) / 10
        times[f].append(t)
print(args)
for f in funcs:
    print(stats(f), f.__name__)

print('\nPython:', sys.version)