#!/usr/bin/env python3

from collections import Counter
from itertools import islice
from typing import Any, Iterator, List, Mapping, Sequence


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


def population_counts(lst: List[Any]) -> Mapping[Any, int]:
    """
    Return a population count mapping for the list (i.e. the keys are
    list items and the values are the number of occurrances of that
    list item in the original list.

    >>> population_counts([1, 1, 1, 2, 2, 3, 3, 3, 4])
    Counter({1: 3, 3: 3, 2: 2, 4: 1})

    """
    return Counter(lst)


def most_common_item(lst: List[Any]) -> Any:

    """
    Return the most common item in the list.  In the case of ties,
    which most common item is returned will be random.

    >>> most_common_item([1, 1, 1, 2, 2, 3, 3, 3, 3, 4, 4])
    3

    """
    return population_counts(lst).most_common(1)[0][0]


def least_common_item(lst: List[Any]) -> Any:
    """
    Return the least common item in the list.  In the case of
    ties, which least common item is returned will be random.

    >>> least_common_item([1, 1, 1, 2, 2, 3, 3, 3, 4])
    4

    """
    return population_counts(lst).most_common()[-1][0]


def dedup_list(lst: List[Any]) -> List[Any]:
    """
    Remove duplicates from the list performantly.

    >>> dedup_list([1, 2, 1, 3, 3, 4, 2, 3, 4, 5, 1])
    [1, 2, 3, 4, 5]

    """
    return list(set(lst))


def uniq(lst: List[Any]) -> List[Any]:
    """
    Alias for dedup_list.

    """
    return dedup_list(lst)


def ngrams(lst: Sequence[Any], n):
    for i in range(len(lst) - n + 1):
        yield lst[i:i + n]


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