The stable version (3.1.3) in the Debian Stretch repository is kind of old (https://packages.debian.org/search?keywords=spyder3).
So, I installed the 3.2.6 version via pip3 install spyder --user.
How can I run it? Tried: spyder, spyder3, python3-spyder python3 spyder. It was installed correctly and can be imported into an interactive shell.