Remove all usage of six

[Anutrix]

Resolves or helps resolve #29.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[ricea]

Thanks! Unfortunately I won't have time to finish reviewing this this week. I should be able to do it Monday or Tuesday.

[Anutrix]

Thanks! Unfortunately I won't have time to finish reviewing this this week. I should be able to do it Monday or Tuesday.

Please take your time.

On an unrelated note. Pipeline is failing as ubuntu-latest 24.04 doesn't support Python 3.7 which has reached end-of-life. See actions/setup-python#962.
Would Python 3.7 be removed from github actions or is ubuntu-latest gonna be changed to ubuntu-22.04?

[quasi-mod]

Thanks for working on this!
Overall LGTM :)

[ricea]

On an unrelated note. Pipeline is failing as ubuntu-latest 24.04 doesn't support Python 3.7 which has reached end-of-life. See actions/setup-python#962. Would Python 3.7 be removed from github actions or is ubuntu-latest gonna be changed to ubuntu-22.04?

Please remove Python 3.7 from github actions, and add 3.8 (or 3.9 if 3.8 is also no longer supported). IIRC our aim is to test the oldest version we support and the two newest stable versions. Since this will be a new major version dropping Python 3.7 support is reasonable.

[Anutrix]

On an unrelated note. Pipeline is failing as ubuntu-latest 24.04 doesn't support Python 3.7 which has reached end-of-life. See actions/setup-python#962. Would Python 3.7 be removed from github actions or is ubuntu-latest gonna be changed to ubuntu-22.04?

Please remove Python 3.7 from github actions, and add 3.8 (or 3.9 if 3.8 is also no longer supported). IIRC our aim is to test the oldest version we support and the two newest stable versions. Since this will be a new major version dropping Python 3.7 support is reasonable.

Cool. 3.9 is oldest supported version. Newest versions released stable versions are 3.12 and 3.13 released on 2023 Oct and 2024 Oct. So I changed it from 3.7, 3.10, 3.11 to 3.9, 3.12, 3.13.
Source: https://devguide.python.org/versions/

Let me know if you want me to make a separate PR or leave the newer versions unchanged.