GTK protocol error
Problem
If you are running as a root user while opening a GTK session on Linux i.e. using sudo, su, etc, you might encounter errors like:
No protocol specified
/usr/lib64/python2.7/site-packages/gtk-2.0/gtk/__init__.py:57: GtkWarning: could not open display
warnings.warn(str(e), _gtk.Warning)
No protocol specified
Unable to initialize gtk: could not open display, falling back to console.
Why it occurs
This occurs generally due to Wayland. The root user does not have permissions to run programs in the current session.
Solution
Run xhost + local: to allow other users (including root) to run programs in the current session.
Try running your program again now, it should work!