How to install GTK2 / PyGTK on Ubuntu 20.04?

[MartinThoma]

I keep getting an error message:

$ ./w3af_gui
The GTK package requirements are not met, please make sure your system meets these requirements:
    - PyGTK >= 2.12
    - GTK >= 2.12

I think I have GTK installed:

$ dpkg -l libgtk2.0-0 libgtk-3-0 python-gi
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name              Version          Architecture Description
+++-=================-================-============-=======================================================
ii  libgtk-3-0:amd64  3.24.20-0ubuntu1 amd64        GTK graphical user interface library
ii  libgtk2.0-0:amd64 2.24.32-4ubuntu4 amd64        GTK graphical user interface library - old version
ii  python-gi         3.36.0-1         amd64        Python 2.x bindings for gobject-introspection libraries

What do I need to do to get the required versions?