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import random

getrandbits = random.SystemRandom().getrandbits

DEFAULT_ALPHABET = ("0123456789"
                    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                    "abcdefghijklmnopqrstuvwxyz")

def get_random_word(length, alphabet=DEFAULT_ALPHABET):
    remainder = getrandbits(length * 8)
    return encode_word(remainder, alphabet=alphabet)

def encode_word(number, alphabet=DEFAULT_ALPHABET):
    base = len(alphabet)
    digits = []
    append = digits.append
    quotient = number
    while True:
        quotient, remainder = divmod(quotient, base)
        append(alphabet[remainder])
        if quotient <= 0:
            break

    return ''.join(digits)