I am using ubuntu 12.04 and I am trying to pip install virtualenv but suddenly I got this error.
samuel@sampc:~$ pip install virtualenv Downloading/unpacking
It's because the virtual environment viarable has not been installed.
Try this:
sudo pip install virtualenv virtualenv --python python3 env source env/bin/activate pip install
or
sudo pip3 install virtualenv virtualenv --python python3 env source env/bin/activate pip3 install