python - 在terminal中启动程序时，为何会出现未导入包的错误？

如果直接右键运行程序，并不会出现这样的问题，之后我尝试在terminal中使用pip install导入包，却出现错误信息：

error: [Errno 13] Permission denied: '/Library/Python/2.7/site-packages/itsdangerous.py'
    
    ----------------------------------------
Command "/usr/bin/python -u -c "import setuptools, tokenize;__file__='/private/var/folders/v8/xx0fb7451z76_f99ffxshtdh0000gn/T/pip-build-QwdTFU/itsdangerous/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /var/folders/v8/xx0fb7451z76_f99ffxshtdh0000gn/T/pip-dh5YgM-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /private/var/folders/v8/xx0fb7451z76_f99ffxshtdh0000gn/T/pip-build-QwdTFU/itsdangerous/