Neither 'setup.py' nor 'pyproject.toml' found.

Question

$ sudo pip install --target= ~/Downloads/ROPgadget capstone
ERROR: Directory '/home/XXX/Downloads//ROPgadget' is not installable. Neither 'setup.py' nor 'pyproject.toml' found.

ubuntu20上用pip安装东西时候遇到这个报错怎么办，网上都没有太多有用的办法，是要重装python吗（怎么装快点）
pip升级也报错：Defaulting to user installation because normal site-packages is not writeable
请大家帮忙！