如何合并两个文件，使相等的行不会重复？

def merge_files(file1, file2, output_file):
    # 读取文件1的内容
    with open(file1, 'r') as f1:
        lines1 = f1.readlines()

    # 读取文件2的内容
    with open(file2, 'r') as f2:
        lines2 = f2.readlines()

    # 合并文件并去重
    merged_lines = []
    for line in lines1:
        if line not in lines2 and line not in merged_lines:
            merged_lines.append(line)
    for line in lines2:
        if line not in merged_lines:
            merged_lines.append(line)

    # 将合并后的内容写入新文件
    with open(output_file, 'w') as f:
        f.writelines(merged_lines)

# 调用示例
merge_files('file1.txt', 'file2.txt', 'merged_file.txt')