如何复制文件而不擦除目标文件夹中的复制不关心的文件

import os
import shutil

def copy_files(source_folder, target_folder):
    for root, dirs, files in os.walk(source_folder):
        for file in files:
            source_file_path = os.path.join(root, file)
            target_file_path = os.path.join(target_folder, file)
            
            # 判断文件类型，可以根据后缀名进行判断
            if file.endswith('.txt') or file.endswith('.doc') or file.endswith('.pdf'):
                # 复制文件
                shutil.copyfile(source_file_path, target_file_path)

source_folder = '/path/to/source/folder'  # 源文件夹路径
target_folder = '/path/to/target/folder'  # 目标文件夹路径

copy_files(source_folder, target_folder)