Метод readline() — как прочитать случайные строки из txt-файла?

import smtplib
import random
from smtplib import SMTP_SSL
import email
from email.mime.multipart import MIMEMultipart
from email.mime.base import MIMEBase
from email.mime.text import MIMEText
from email import encoders
import os
import sys, traceback
import time
from time import gmtime, strftime
 
c = 0
files = [
  'C://Users//test//Downloads//1_Amanda-De-Cadenet.jpg',
  'C://Users//test//Downloads//0_a82a7_7db42dad_orig.jpg',
  'C://Users//test//Downloads//GildaAmbrosio-1.jpg',
  'C://Users//test//Downloads//gilda20140223-4844-2.jpg'
]

answers = ['y', 'да', 'YES', 'yes', 'Y']
sender_address = 'test.test.12@bk.ru' 
receiver_address = 'test.test.12@bk.ru' 

#открываем файл
f = open("C:\\Users\\test\\Desktop\\spam.txt")

def send(): 
    global c         
    date = strftime("%H:%M:%S")
   
   try:
        while True:
            
            for i, filename in enumerate(files):
                path = random.choice(files)
                    
                if not os.path.isfile(path):
                    print("Неверный путь к файлу")
                    continue
                else:
                    filename = os.path.basename(path)
                         
                    basename = os.path.basename(files[i])
                    #Receiver email

                    sender_address = 'test.test.12@bk.ru'
                           
                    #Compose attachment
                    part = MIMEBase('application', "octet-stream")
                    part.set_payload(open(files[i], "rb").read())
                    encoders.encode_base64(part)
                    part.add_header('Content-Disposition', 'attachment; filename = "%s"' % basename)
                                
                    #Compose message
                    msg = MIMEMultipart()
                    #Header \\ заголовок письма    
                    msg['Subject'] = f.readline()[0:85] #строка создающая заголовок
                    msg['From'] = sender_address
                    msg['To'] = receiver_address
                    msg.attach(part)
                    
                    #Send mail
                    smtp = smtplib.SMTP('smtp.mail.ru', 25)
                    smtp.ehlo()
                    smtp.starttls()
                    
                    smtp.login(sender_address, 'test')
                    smtp.sendmail(sender_address, receiver_address, msg.as_string())
                    c += 1
                    print('%s sent to: %s ' % (filename, receiver_address), c, '\n')
    except Exception:
        print(traceback.format_exception(*sys.exc_info())[1])
        input("End ")


def sendFileByFile():
    for i, filename in enumerate(files):
        path = filename
        filename = os.path.basename(path)

    global c

    global sender_address
    
    r_address = input("спамить на мыло: %s\nфайлом %s? --->>> " % (receiver_address, filename))
    if r_address in answers: 
        send() 
    if not r_address:
        send()

sendFileByFile()