Generate unique key with django model

model_utils.py

import string
from random import SystemRandom

def generate_key(field_name, model, size=8):
    charset = string.ascii_lowercase + string.digits
    key = ''.join(SystemRandom().choice(charset) for _ in range(size))
    is_exist = model._default_manager.filter(**{field_name: key}).exists()

    while is_exist:
        key = generate_key(size, model)
    return key