当处理随机模块时，字符串索引超出范围

我正在python中创建密码生成器，这是我遇到的错误。这是我的代码:

import random

symbols = 'qwertyuiopasdfghjklzxcvbnm'
choosing_len = int(input('> '))


def password_generating():

    def random_letter():
        zero = 0
        lenght = len(symbols)
        letter_index = random.randint(zero, lenght+1)
        random_symbol = symbols[letter_index]

        return random_symbol


    password = []

    while len(password) != choosing_len:
        key = [random_letter()]
        password = password + key

    print(''.join(password))


password_generating()

我不得不说这个错误是随机出现的(它几乎不会在6中出现)。没有什么帮助。 问题来源StackOverflow 地址：/questions/59378424/indexerror-string-index-out-of-range-while-working-with-random-module