Introduction to computer algebra systems? [closed]

Answer 1

You mention SymPy in your question so I'll speak to that briefly.

The project and community of SymPy are themselves actually very good resources.

1. There is a variety of expertise that regularly checks and responds to the mailing list.
2. The code is openly available on github.
3. The documentation is fairly complete and often includes academic citations.

If you're interested in CASs come on by. The contributors like to talk about what they work on. If you're interested it's easy to get started and add your own contributions.