> How will you avoid having two variants of each and every lib ?

The python community is also struggling with this problem. The emerging approach, which seems to me to be the right approach, is to write the libraries such that they do not do any IO; then you can use them anywhere, with some integration. So basically it's just the principle of separation of concerns.

See more here: https://sans-io.readthedocs.io/how-to-sans-io.html