import random


def random_number_generator(size=4, chars='1234567890'):
    """[Generates random number]

    Args:
        size (int, optional): [size of number to generate]. Defaults to 4.
        chars (str, optional): [numbers to use]. Defaults to '1234567890'.

    Returns:
        [str]: [Generated random number]
    """
    return ''.join(random.choice(chars) for _ in range(size))