随机验证码生成（python实现）

需求：生成随机不重复验证码。

代码：

#!/usr/bin/env python
# encoding: utf-8
"""
@author: 侠之大者kamil
@file: 200number.py
@time: 2016/4/13 23:33
"""
import random,string
def rand_str(num,length = 7):
    f = open("Activation_code2.txt","wb")
    for i in range(num):
        chars = string.ascii_letters + string.digits
        s = [random.choice(chars) for i in range(length)]
        f.write(bytes((''.join(s)  + '\n' ), 'utf-8')) #f.write(''.join(s) + '\n')   py2
    f.close()
if __name__=="__main__":
    rand_str(200)

会逐行写在文件里，涉及知识点：f.open  f.writer random

#’str’ does not support the buffer interface  在python3 报错
with open("test.txt") as fp:
    line = fp.readline()
with open("test.out", 'wb') as fp:
    fp.write(line)


#解决方案1  在Python3x中需要将str编码,
with open("test.txt") as fp:
    line = fp.readline()
with open("test.out", 'wb') as fp:
    fp.write(bytes(line, 'utf-8'))
#解决方案2 不想用b(binary)模式写入，那么用t(text, 此为写入的默认模式)模式写入可以避免这个错误.
with open("test.txt") as fp:
    line = fp.readline()
with open("test.out", 'wt') as fp:
# with open("test.out", 'w') as fp:
    fp.write(line)