ImportError: No module named IPython.frontend.terminal.ipapp

(a-virtualenv)me@pc:~$ ipython
Traceback (most recent call last):
  File "/usr/bin/ipython", line 19, in 
    from IPython.frontend.terminal.ipapp import launch_new_instance
ImportError: No module named IPython.frontend.terminal.ipapp

This problem may happen to you for some reason. To work around this, I add this to my /usr/bin/ipython

import sys
if "/usr/lib/python2.7/dist-packages" not in sys.path:
    sys.path.append("/usr/lib/python2.7/dist-packages")

This trick works for Balthazar.