用Python替换文件中的一行并不能正常工作

import os

def replace_line(file_path, line_number, new_line):
    # 检查文件是否存在
    if not os.path.exists(file_path):
        return "文件不存在"

    # 检查文件权限
    if not os.access(file_path, os.W_OK):
        return "没有写入权限"

    # 打开文件并替换指定行
    with open(file_path, 'r') as file:
        lines = file.readlines()

    if line_number < 1 or line_number > len(lines):
        return "行号超出范围"

    lines[line_number - 1] = new_line + os.linesep

    with open(file_path, 'w') as file:
        file.writelines(lines)

    return "替换成功"

# 示例用法
file_path = "example.txt"
line_number = 3
new_line = "This is the new line"

result = replace_line(file_path, line_number, new_line)
print(result)