#!/usr/bin/env python3

import random
from typing import Iterable, List, Optional, Set


class grab_bag(object):
    def __init__(self) -> None:
        self.contents: Set[str] = set()

    def clear(self) -> None:
        self.contents.clear()

    def add(self, item: str) -> None:
        if item not in self.contents:
            self.contents.add(item)

    def add_all(self, collection: Iterable[str]) -> None:
        for x in collection:
            self.add(x)

    def subset(self, count: int) -> Optional[List[str]]:
        if len(self.contents) < count:
            return None
        subset = random.sample(self.contents, count)
        return subset

    def size(self) -> int:
        return len(self.contents)


# x = grab_bag()
# x.add_all([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
# print x.subset(3)