[IPython-User] What would cause empty output cache? And how to fix it?
IPython3 worked fine so I installed jupyter, qtconsole. While I was
using jupyter, qtconsole back and forth, I noticed qtconsole stopped
showing [Out ##] prompt. It only showed the output result of input cell.
And IPython 4.0.1 also stopped caching output cells and I couldn't use
the default variables, _, __, ___, and _[number].
I played with configuration variables that related to caching and
history for hours in vain. Reinstallation of IPython 4.0.1 fixed it