# Iterators and iterables

import rand

def is_iterable(value): return getattr(value, '__iter__', False)

# Sentinel to use in iter() if function return value should be ignored.

# Can't use object() because iter() compares sentinel using ==.

iter_end = rand.rand_int()

def func_iter(func):

    '''Used to iterate a generating function which raises StopIteration instead

    of returning a sentinel value'''

    return iter(func, iter_end)

def consume_iter(iter_):

    for elem in iter_: pass

def flatten(outer_iter):

    if is_iterable(outer_iter):

        for iter_ in outer_iter:

            if is_iterable(iter_):

                for el in iter_: yield el

            else: yield iter_

    else: yield outer_iter

def flatten_n(outer_iter, depth=2):

    if depth < 2: return outer_iter

    elif depth == 2: return flatten(outer_iter)

    else: return flatten(flatten_n(outer_iter, depth-1))