How do I fix melds 'Cannot import: GTK+' error caused by missing 'gi.repository'?

Question

I\'ve recently started learning GTK+ development and installed some new packages (I don\'t remember which ones). Now the merge tool meld doesn\'t work any more:

Answer 1

I just encountered this - but forgot that I was working inside a virtualenv that didn't have this stuff installed. Just needed to run the command from outside the virtualenv.