Python random generate random passwords

import random
def  RandomPw(n=20):
    s = ''
    for i in range(n):
        list = ['.',',','?','*','+','-','_','/','<','>','~','!','#','@','$','%','^','&','(',')','=','[',']','{','}','|',':']
        digit = str(random.randint(0,9))
        char_upper = str(chr(random.randint(65,90)))
        char_lower = str(chr(random.randint(97,122)))
        char = str(random.choice(list))
        res = [digit,char_lower,char_upper,char]
        result = random.choice(res)
        s += result
    return  s
a = RandomPw()
print(a)