How to use reuse-tool on Trisquel and similar without pip?

As far as I understand, the problem with pip is that it recommends non-free software, which is against the free software distribution guidelines. Still, the free Python packages are usually in Trisquel's repository, but if reuse requires versions newer than those in Trisquel's repository it may not work.

However, did you try the Guix package for reuse? Guix is easy to use on Trisquel (even though it seems it is taking a lot of disk space and network bandwidth at every update).

EDIT: I don't know how you are personally involved in https://dedriver.org, LibreJS blocks https://dedriver.org/main.bundle.js as it can't find the license. I found some headers in it that file mentioning license but nothing about most of the contents. I don't know whether it is that the license information was forgotten or that there is no license (which means it is not free software).