isympy3 software package provides Python3 shell for SymPy, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install isympy3
isympy3 is installed in your system.
Make ensure the isympy3 package were installed using the commands given below,
$ sudo dpkg-query -l | grep isympy3 *
You will get with isympy3 package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Python |
| Package | isympy3 |
| Version | 1.0-2 |
| Description | Python3 shell for SymPy |
| Sub Section | Python |