Python：重复拷目录时，`copytree(..., dirs_exist_ok=True)` 能省掉很多判断

有些小脚本就是会反复把一份目录拷到目标路径。

环境：Python 3.8+，只用标准库。保存为 copytree-demo.py：

from pathlib import Path
from tempfile import TemporaryDirectory
from shutil import copytree

with TemporaryDirectory() as src, TemporaryDirectory() as dst:
    src_root = Path(src)
    dst_root = Path(dst)

    (src_root / 'a.txt').write_text('hello', encoding='utf-8')
    (src_root / 'sub').mkdir()
    (src_root / 'sub' / 'b.txt').write_text('world', encoding='utf-8')

    target = dst_root / 'backup'
    copytree(src_root, target, dirs_exist_ok=True)
    copytree(src_root, target, dirs_exist_ok=True)

    print(sorted(str(p.relative_to(target)) for p in target.rglob('*') if p.is_file()))

这样目标目录已经存在时也能继续拷，不用先手动判断一遍。