cython3 software package provides C-Extensions for Python 3, you can install in your Debian 8 (Jessie) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install cython3
cython3 is installed in your system.
Make ensure the cython3 package were installed using the commands given below,
$ sudo dpkg-query -l | grep cython3 *
You will get with cython3 package name, version, architecture and description in a table
| Distro | Debian 8 jessie |
| Section | Python |
| Package | cython3 |
| Version | 0.21.1-1 |
| Description | C-Extensions for Python 3 |
| Sub Section | Python |