All you need to do is to install the tkinter package. Now universal precompiled packages such as ActivePython will not work, well at least it didn’t work for me. I don’t know if this problem occurs in other OSes but I know the solution for Linux: install the Tk package from a repository.
In Arch, Tk is available in the Arch repository. You don’t need aur for this, just type on the terminal:
sudo pacman -S tk
If you are on a Debian, Ubuntu or another Debian-based distro, just type on the terminal:
sudo apt-get install tk
On Fedora:
sudo dnf install tk
Tk is not to be mistaken with python-tk, which is a package for Python 2 (you shouldn’t need it unless you are working with legacy code).