do you mind squashing?

Please follow CONTRIBUTING.md and manual#submitting-changes-making-patches and squash the fix-up commits.

This can be done without git rebase -i by doing:

git reset HEAD~1                    # move fix-up commits into unstaged
git add -- pkgs/                    # move changes into staged
git commit --amend --no-edit        # add changes to previous commit
git push ... ... --force            # modify current PR branch

However, git rebase -i is a more powerful alternative, I created a small video demonstrating it's use here. A more indepth text tutorial can be found here

do you mind squashing?

I am squashing it at the moment. Easiest thing how to accept your suggestions in my local branch is to accept them via Github UI into remote branch and then update my local branch.

in all-packages, i would would just do python = python3;

What do you mean by this? This changeset does not touch all-packages ...

I guess you meant this, right? (in pkgs/top-level/python-packages.nix - included in 574c7d9)

-  ovito = toPythonModule (pkgs.libsForQt5.callPackage ../development/python-modules/ovito { });
+  ovito = toPythonModule (pkgs.libsForQt5.callPackage ../development/python-modules/ovito { inherit python; });

sorry, for some reason I thought there was a top-level ovito

oh in the original list, it just shows ovito, but that's likely because it's just taking the derivation name.