There is a great tutorial at:
https://seanmcgrath.blogspot.com/JythonWebAppTutorialPart1.html#InstallingJython

Also great tutorial at https://www.tutorialspoint.com/jython/jython_eclipse_plugin.htm

1. Install Jython 2.7 - From: http://www.jython.org/downloads.html
2. Download the jython-standalone.jar
3. To run the installer, exit to a console window and use: 
     java -jar jython-installer-2.7.0.jar (a GUI window will appear)
4. Install the "standard core" default option
5. Make sure you have Eclipse "Neon" or above 
6. Also need JDK 8 or above (JVM 1.8 or above)
7. Install PyDev into Eclipse - http://www.jython.org/jythonbook/en/1.0/JythonIDE.html
8. Create a new Web Application
9. Drag jython-standalone-2.7.0.jar to the WEB-INF/LIB folder or configure the build-path
10. Update the web.xml deployment descriptor to invoke python when called
11. Use the JythonTest.zip sample project to get web.xml template with proper info
12. Run the project on the tomcat server.