Calling IPython from a virtualenv

I understand that IPython is not virtualenv-aware and that the most logical solution to this is to install ipython in each virtualenv seperately using

    pip install ipython

So far so good. One thing I noticed is that if the system-wide copy of IPython is called from within a virtualenv using $> ipython before IPython is installed under this virtualenv, subsequent $> ipython commands will continue to bring up the system-wide ipython copy.

On the other hand, if ipython is not called prior to installing it under a virtualenv $> ipython will bring up the newly installed copy.

What is the explanation for this?

It also makes me wonder if this behavior means I should expect some trouble down the way?

alias ipy="python -c 'import IPython; IPython.terminal.ipapp.launch_new_instance()'"

This is a great way of always being sure that the ipython instance always belongs to the virtualenv's python version.

This works only on ipython >2.0.