import random
import string


def random_string(length: int) -> str:
    """Returns a string of random characters of length 'length'
    :param length: How long the string to return must be
    :type length: int
    :returns: an alpha-numerical string of specified length with random characters
    :rtype: str
    """
    return ''.join(random.choice(string.ascii_lowercase + string.digits) for _ in range(length))