def count(start=0, step=1):
    while True:
        yield start
        start += step

def cycle(p):
    try:
        len(p)
    except TypeError:
        # len() is not defined for this type. Assume it is
        # a finite iterable so we must cache the elements.
        cache = []
        for i in p:
            yield i
            cache.append(i)
        p = cache
    while p:
        yield from p


def repeat(el, n=None):
    if n is None:
        while True:
            yield el
    else:
        for i in range(n):
            yield el

def chain(*p):
    for i in p:
        yield from i

def islice(p, start, stop=(), step=1):
    if stop == ():
        stop = start
        start = 0
    # TODO: optimizing or breaking semantics?
    if start >= stop:
        return
    it = iter(p)
    for i in range(start):
        next(it)

    while True:
        yield next(it)
        for i in range(step - 1):
            next(it)
        start += step
        if start >= stop:
            return

def tee(iterable, n=2):
    return [iter(iterable)] * n