Copyright of modifications and derivative works of Python License 2 licensed software

Question

I am writing a Python package in which I plan to vendorize a modified copy of part of another package that was released under Python License 2 (it is not part of the PSL and not subject to any other licenses). The license allows producing "derivative works",

2. ... provided, however, that this License Agreement and {Licensor}'s notice of copyright, i.e., "Copyright (c) 2001-2019 {Licensor}; All Rights Reserved" are retained in {Software} alone or in any derivative version prepared by Licensee.

3. In the event Licensee prepares a derivative work that is based on or incorporates {Software} or any part thereof, and wants to make the derivative work available to others as provided herein, then Licensee hereby agrees to include in any such work a brief summary of the changes made to {Software}.

My questions are:

1. In my modified version of the vendorized code, do I retain copyright to my modifications? Can I put a notice such as "Modifications Copyright (c) 2019 ipetrik" after the required "brief summary of changes"?

2. Can I license my changes and any of my own files not incorporating any code from the Python License 2 licensed software under a different license, such as Apache or MIT?

Answer 1

1. In my modified version of the vendorized code, do I retain copyright to my modifications? Can I put a notice such as "Modifications Copyright (c) 2019 ipetrik" after the required "brief summary of changes"?

You always own the copyrights on code you write, even if it is a modification of code owned by others, except

1. if you have signed a contract to transfer copyright ownership
2. you write the software as part of your employment contract (your employer owns the copyrights).

If you have made large enough changes to write a meaningful "brief summary of changes", then it is entirely acceptable to add your own copyright notice.

2. Can I license my changes and any of my own files not incorporating any code from the Python License 2 licensed software under a different license, such as Apache or MIT?

The Python License you quote appears to be a permissive license, so it places few restrictions on you and how you can license your own code.

However, I would recommend against using different licenses for code that lives in the same project, because it is hard to properly indicate which parts of the code are subject to which license. This problem only becomes harder if you try to apply different licenses to different parts of a single file.