Which package installation methods to use inside a python virtual environment?

[python_user_03]

I am using virtualenv. I know that using pip install <package_name> inside a python virtual environment will isolate that package (the package is only to be found inside the virtual environment). What about installing a package inside a python virtual environment using these methods: sudo pip install, sudo apt-get install, or building the package from source? Will they isolate the package? is the package going to be installed on the whole system?