我不确定我是否完全理解你的问题，但我建议使用itertools进行简化：

with open('username.csv') as f:
    reader = csv.reader(f)
    # substitute your values
    starting_points = [random.randint(0, 5) for i in range(3)] 
    for sp in starting_points:
        print('random starting line:', sp)
        skipped_lines = itertools.islice(reader, sp - 1)
        next(skipped_lines, None)
        line = next(reader)
        print(line)

干杯：）

试试这个：

from telethon.sync import TelegramClient
from telethon.sessions import StringSession
from telethon import functions, types
from keep_alive import keep_alive
import asyncio
import os
import time
import fileinput
import random
import csv
from telethon import errors
from telethon.sync import TelegramClient

api_id = input("API ID: ")
api_hash = input("API HASH: ")
correct_channel = input("CORRECT CHANNEL: ")

ses_string = os.getenv('ses_string')
keep_alive()

starting_points = [random.randint(0, 5) for i in range(3)]
read_nbr_of_lines = 2

for sp in starting_points:
    print('random starting line: %s'%sp)
    read_lines = 0
    with open('username.csv') as cf:
        lines = csv.reader(cf)
        for nbr, line in enumerate(lines):
            if nbr < sp - 1: continue
            read_lines += 1
            if read_lines > read_nbr_of_lines: break
            print(nbr, line)

random_user = line[0]
print('A randomly selected username is:', random_user)

with TelegramClient(StringSession(ses_string), api_id, api_hash) as client:
    while True:
        try:
            time.sleep(10)
            result = client(functions.channels.UpdateUsernameRequest(
               channel= correct_channel ,
               username = random_user
            ))
        except Exception as e:
            print(type(e), str(e))

因为line是一个列表，所以你可以使用line[0]来获取第一个也是唯一一个字符串，或者将其赋值给一个新的变量random_user并在代码中使用它。