import random


def randomword(length=12):
    """
    Generate a string of random alphanumeric characters
    """
    valid_chars = \
        'abcdefghijklmnopqrstuvyxwzABCDEFGHIJKLMNOPQRSTUVYXWZ012345689'
    return ''.join(random.choice(valid_chars) for i in range(length))