I have been trying to install various modules that I need to have to run this script:
https://github.com/austingandy/slack-evernote/blob/master/slackwriter.py
<While it is possible to migrate a script from Python 2 to Python 3, doing it right isn't trivial. You could try using 2to3 but I suspect it won't quite do the job.
The easiest is to just use virtualenv with Python 2. I'm not sure how it is on Mac but on Linux you can just have both versions of Python installed in parallel and you can pick the one you need in your virtualenv as e.g.
virtualenv -p python2 venv
where python2 is your Python 2 binary and venev the directory you want tot install the virtualenv into.
Where you might run into trouble is the activate scripts which are only available for specific shells. However, you could probably adapt one if none works out of the box.
AFAIK, Evernote SDK for Python 3 is not yet supported.
https://github.com/evernote/evernote-sdk-python3
This is a test SDK! The official Evernote SDK for Python doesn't support Python 3 yet; this repository is an experiment as we try to migrate.
You can try installing manually from the link above or downgrade to python2 in your virtual env.