#!/usr/bin/env python3

from itertools import islice
from typing import Any, Iterator, List


def shard(lst: List[Any], size: int) -> Iterator[Any]:
    """
    Yield successive size-sized shards from lst.

    >>> for sublist in shard([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12], 3):
    ...     [_ for _ in sublist]
    [1, 2, 3]
    [4, 5, 6]
    [7, 8, 9]
    [10, 11, 12]

    """
    for x in range(0, len(lst), size):
        yield islice(lst, x, x + size)


def flatten(lst: List[Any]) -> List[Any]:
    """
    Flatten out a list:

    >>> flatten([ 1, [2, 3, 4, [5], 6], 7, [8, [9]]])
    [1, 2, 3, 4, 5, 6, 7, 8, 9]

    """
    if len(lst) == 0:
        return lst
    if isinstance(lst[0], list):
        return flatten(lst[0]) + flatten(lst[1:])
    return lst[:1] + flatten(lst[1:])


def prepend(item: Any, lst: List[Any]) -> List[Any]:
    """
    Prepend an item to a list.

    >>> prepend('foo', ['bar', 'baz'])
    ['foo', 'bar', 'baz']

    """
    lst.insert(0, item)
    return lst


if __name__ == '__main__':
    import doctest
    doctest.testmod()