python_生成随机手机号

写个一函数，这个函数的功能是，传入一个数字，产生N条手机号，产生的手机号不能重复。
[150,189,188,170,132,150,186]
def phone(500):
phone.txt
1861232323
23423423

import random
import string
#写一个文件
def phone_num(num):
    phone_nums=set()#集合不重复，无序
    num_start = ['131','132','133','150','186','189','177']
    for i in range (num):
        num_starts =random.choice(num_start)
        num_end =''.join(random.sample(string.digits,8))
        res = num_starts+num_end+'
'
        # print("num_start is {} 	 num_end is {}".format(num_starts,num_end))
        #将生成的手机号添加到集合
        phone_nums.add(res)
    with open('phone_nums.txt','w',encoding='utf-8') as fw:
        fw.writelines(phone_nums)
phone_num(10)