在stackoverflow上看到这样的问题：

需要用python生成由数字和大写字母组成的随机字符串，如：

• 6U1S75
• 4Z4UKK
• U911K4

这个需求可以用一行python语句解决：

''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(N))

当然，上面的语句存在一个问题。This is an excellent method, but the PRNG in random is not cryptographically secure. I assume many people researching this question will want to generate random strings for encryption or passwords. You can do this securely by making a small change in the above code:

''.join(random.SystemRandom().choice(string.uppercase + string.digits) for _ in xrange(n))

Using random.SystemRandom() instead of just random uses /dev/urandom on *nix machines and CryptGenRandom() in Windows. These are cryptographically secure PRNGs. Using random.choice instead of random.SystemRandom().choice in an application that requires a secure PRNG could be potentially devastating, and given the popularity of this question, I bet that mistake has been made many times already.