import math
import random


def _get_random_string(size):
    """Get random string of given size."""
    if not size:
        return ""

    chars = "abcdefghijklmnopqrstuvwxyz"
    chars *= int(math.ceil(size / len(chars)))
    chars = list(chars[:size])
    random.shuffle(chars)
    return "".join(chars)