How to install pygtk 3 on Mac OS X?

What I tried:

brew install pygobject3 --with-python@2 gtk+3
brew install pygtk3
brew install pygobject3
pip install pygobject

python -c 'import gi; gi.require_version("Gtk", "3.0")'

Result:

ValueError: Namespace Gtk not available for version 3.0

Note that I'm running conda, with python 3.6; and Mac OS X High-Sierra

I read through the following questions/answers before posting:

(Note that if I change the requires to 2.0, then it loads ok, but I get a warning:

"RuntimeWarning: You have imported the Gtk 2.0 module. Because Gtk 2.0 was not designed for use with introspection some of the interfaces and API will fail. As such this is not supported by the pygobject development team and we encourage you to port your app to Gtk 3 or greater. PyGTK is the recomended python module to use with Gtk 2.0" )

Solution

The problem is that the developers of pygobject3 have written their install instructions that does NOT consider pip/conda. If you follow the official documentation:

Have to use the homebrew python installation (the one installed when you go brew install python)
brew install gtk+3 is NOT compatible with non homebrew Pip/Conda python installs. You have to build the GTK3 package manually to use the pip version of pygobject3.

However if you want to use conda, thanks to this conda contributor, there is a pre-built conda gtk3 package you can use, you just have to get it from his channel:

Make a new environment using conda:

conda create --name my_env

install pygobject3 from conda

conda install pygobject

install gtk3 from the pkgw-forge channel

conda install -c pkgw-forge gtk3

To verify, open python from within the conda env and run

import gi
gi.require_version("Gtk", "3.0")

Should get no errors