Setting up developement environment: PyCharm, python-gtk, windows

use 32 or 64 Bit version of Python?

The documentation suggests 32 bit for msys2, so this is the safest. However, if you have a 64 bit computer, the 64 bit version could allow some more processing power for larger tasks.

How to install gtk for python (pip or exe)?

Most definitely using the .exe available from this source. This tool is a package manager for Windows that will let you install gtk and its dependencies. Instructions there will walk you through setting up the default environment, then from that environment run pacman -Suy and pacman -S mingw-w64-i686-gtk3 mingw-w64-i686-python2-gobject mingw-w64-i686-python3-gobject.

Use virtual env in PyCharm or use "Existing Interpreter"?

Using the 'Existing Intepreter' is a must for this method of installation, as you need to point PyCharm to your msys2 Python, which actually has gtk available. It should be located at C:\msys64\bin\python.exe. Keep in mind that you might not be able to run some scripts directly through PyCharm this way, as Python will be running through a virtual bash-like environment. Save your scripts in the C:\msys64\home\<username> directory so that you can run them easily when you open msys2 with python3 script.py.

use 32 or 64 Bit version of Python?

You can pick any, it doesn't really matter.

how to install gtk for python (pip or exe)?

You should able to install it with pip: pip install pygtk.

Use virtual env in PyCharm or use "Existing Interpreter"?

If you don't know, you probably need "Existing interpreter". There should be an option to select path to your python.exe It should be there: Menu->File->Settings->Project->Project Interpteter

There two ways of doing what you want.

But first, lets set something straight, when you say gtk, you don't specify GTK-2 or GTK-3. GTK-2 python bindings aka PyGTK is quite an old package (but still possible to use). GTK-3 python bindings, included in PyGobject are, I imagine, what you want.

First option

So, I'll start with the more restrictive one.
You can install PyGObject through the PyGI AllInOne installer. This is a .exe installer that comes with a lot of stuff, from gtk3 and gstreamer, to gnome applications like Glade and Gedit, to non gnome applications. Why do I say it's restrictive? It only works with Python from version 2.7+ to 3.4+ (32 or 64 bits). So if you want to use Python 3.6, you can't use this. And it seems that it will never be updated.

Second option

The other way is using MSYS2, like someone advised before. This option lets you use the current versions of Python supported by mingw-64 repository. Which I believe right now is Python 3.7.
You can install following the steps as described in the PyGObject site. Or the way explained below (CLion).

I don't know how to use PyCharm with a MSYS2 python installation, but a bit of googling led me to this tutorial for CLion. Maybe there's an analog for PyCharm.