密码没有创建到指定的长度？

Question

I am creating a random password generator that takes in a user specified length but I have not been able to create the function in a way that it will make the password exactly that length. I have only been able to do it to multiples of 4 because of the 4 variables I have created. If i was to call the function with a different value like 10, the password would not be length 10. Any suggestions? Also the reason I am dividing by 4 is so that the for loop does not generate a password 4 times the leng.

numbers = '1234567890'
letters = 'qwertyuiopasdfghjklzxcvbnm'
letters_caps = 'QWERTYUIOPLKJHGFDSAZXCVBNM'
symbols = '!@#$%^&*()_+=~`:"<>?|\;,."`'

def create_password(leng):
    password = ''
    lis = []
    for i in range(leng / 4):
        randnum = numbers[random.randrange(0, len(numbers))]
        lis.append(randnum)
        randletter = letters[random.randrange(0, len(letters))]
        lis.append(randletter)
        randletter_cap = letters_caps[random.randrange(0, len(letters_caps))]
        lis.append(randletter_cap)
        randsymbol = symbols[random.randrange(0, len(symbols))]
        lis.append(randsymbol)
    for items in lis:
        password += random.choice(lis)
    print password
create_password(12)

Answer 1

How about this:

numbers = '1234567890'
letters = 'qwertyuiopasdfghjklzxcvbnm'
letters_caps = 'QWERTYUIOPLKJHGFDSAZXCVBNM'
symbols = '!@#$%^&*()_+=~`:"<>?|\;,."`'

import random

raw_psw = numbers + letters + letters_caps + symbols
raw_psw = list(raw_psw)

length = 10
for _ in range(5):
    random.shuffle(raw_psw)
    print("".join(raw_psw[:length]))

cVY;U<,9Fx

$dt_2wx^PJ

9oH|kU~2^g

kJO@n`5H9Z

Y%oEXeOLv3

Answer 2

If you're just concerned about the length and are otherwise happy with your function, the simplest solution would be to round up to the next multiple of four, and then truncate the password before returning it, like:

def create_password(leng):
    password = ''
    for i in range((leng + 3) // 4):
        # add 4 characters however you like
        # ...
    print password[:leng] # truncate to proper length

(As an aside, others have noted that it would be better to use the ''.join() construct rather than append in a loop, it is important to use a secure PRNG to generate passwords, and your code is probably more flexible if you return the password rather than printing it.)

Answer 3

Perhaps the least intrusive change would be to loop exactly the number of times you specify, and call a different function depending on the modulo.

for i in range(leng):
    mod = i % 4
    if mod == 0:
        randitem = numbers[random.randrange(0, len(numbers))]
    elif mod == 1:
        randitem = letters[random.randrange(0, len(letters))]
    elif mod == 2:
        randitem = letters_caps[random.randrange(0, len(letters_caps))]
    else:
        randitem = symbols[random.randrange(0, len(symbols))]
    lis.append(randitem)

This obviously creates a slight skew towards the items towards the beginning of the loop; there is a 75% chance that there will be one more number than there are symbols from the other groups, 50% change for one letter symbol more, etc.

Maybe a better approach would be to choose at random from all groups evenly and accept that true randomness means you will not always receive symbols from every group. This obviously increases the search space for an attacker, because the choice of valid passwords is less constrained.

Answer 4

Just for pass time:

class PasswordGenerator(object):
    def __init__(self, alphabet_classes, r=None):
        from random import SystemRandom
        self.__alphabet_classes = alphabet_classes
        self.__random = r if r else SystemRandom()

    def generate(self, length):
        password = []

        n_classes = len(self.__alphabet_classes)

        idx = [i for i in range(n_classes)]
        self.__random.shuffle(idx)

        for i in range(length):
            password.append(self.__random.choice(self.__alphabet_classes[idx[i % n_classes]]))
        self.__random.shuffle(password)

        return ''.join(password)


if __name__ == '__main__':
    numbers = '1234567890'
    letters = 'qwertyuiopasdfghjklzxcvbnm'
    letters_caps = 'QWERTYUIOPLKJHGFDSAZXCVBNM'
    symbols = '!@#$%^&*()_+=~`:"<>?|\;,."`'
    pg = PasswordGenerator([numbers, letters, letters_caps, symbols])
    for _ in range(5):
        print(pg.generate(1))

So the main loop goes from 1 to n-1 , where n is the length given, in the loop we first decide which set of characters to use, then choose from that set by using random.choice .