Revision history [back]

sudo apt-get install python-catkin-pkg
sudo rm -rf /usl/local/lib/python2.7/dist-packages/catkin*
sudo dpkg -L python-catkin-pkg

This shows you where apt installed catkin_pkg to, this one should be found.
python -c 'import catkin_pkg; print(catkin_pkg.__file__)'

This shows you where it actually finds catkin_pkg, if it is different from the above, delete the folder
python -c 'import sys; print(sys.path)'

This shows you all places where it looks for catkin_pkg

sudo apt-get install python-catkin-pkg
sudo rm -rf /usl/local/lib/python2.7/dist-packages/catkin*/usr/local/lib/python2.7/dist-packages/catkin*
sudo dpkg -L python-catkin-pkg

This shows you where apt installed catkin_pkg to, this one should be found.
python -c 'import catkin_pkg; print(catkin_pkg.__file__)'

This shows you where it actually finds catkin_pkg, if it is different from the above, delete the folder
python -c 'import sys; print(sys.path)'

This shows you all places where it looks for catkin_pkg

UPDATE:

python2.7 finds the installed code at /usr/lib/pymodules/python2.7, As explained by @joq. if you do not see catkin_pkg folder in there, you need to

sudo apt-get install --reinstall python-catkin-pkg