In the previous section you learned how to share a package across several projects, or analyses. However, as your package and analyses evolve asynchronously, it is likely that you will reach a point when you’d like different analyses to use different versions of your package, or different versions of third-party packages that your analysis rely on.
The question is then: how to install two different versions of a same package? And the (short) answer is: you cannot.
If you type pip install numpy==1.18, pip first looks for a version
of numpy already installed (in the site-packages/ directory).
If it finds a different version, say 1.19, pip will uninstall it and
install numpy 1.18 instead.
This limitation is very inconvenient, and is the raison d’être for virtual environments, which we disuss next.