virtualenv is a tool that allows you to install python packages in isolated environments. In this way you can have multiple versions of the same package without interference. I started using this to easily switch between multiple versions of numpy without having to constantly reinstall and update my symlinks. I also did this as a way to install software for Scipy2008, like the Enthought Tool Suite (ETS), in a way that would not effect my current development environment.
This tutorial is based heavily on a blog entry from Prabhu. I’ve extended his shell script to make switching between virtual environments a one-command operation. (Few others who should be credited for encouraging me to use virtualenv: Gael, Jarrod, Fernando)
Download and install the tarball for virtualenv:
tar xzf virtualenv-1.1.tar.gz cd virtualenv-1.1 python setup.py install --prefix=$HOME/local
Note: I install in a local directory, your install location may differ.
Setup a base virtualenv directory. I create this in a local directory, you can do this in a place of your choosing. All virtual environments will be installed as subdirectories in here.:
cd ~/local mkdir -p virtualenv
Create a virtual environment. Here I change into my virtualenv directory and create a virtual environment for my numpy-1.1.1 install:
cd virtualenv/ virtualenv numpy-1.1.1
Set the numpy-1.1.1 as the active virtual environment:
ln -s numpy-1.1.1/bin/activate .
We enable the numpy-1.1.1 virtual environment by sourcing it’s activate script. This will prepend our PATH with the currently active virtual environment.:
# note: still in the ~/local/virtualenv directory source activate
We can see our PATH with the numpy-1.1.1 virtual environment at the beginning. Also not the label of the virtual environment prepends our prompt.:
(numpy-1.1.1)cburns@~ 20:23:54 $ echo $PATH /Users/cburns/local/virtualenv/numpy-1.1.1/bin: /Library/Frameworks/Python.framework/Versions/Current/bin: /Users/cburns/local/bin: /usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/usr/local/git/bin
Then we install numpy-1.1.1 into the virtual environment. In order to install packages in the virtual environment, you need to use the python or easy_install from that virtualenv.:
~/local/virtualenv/numpy-1.1.1/bin/python setup.py install
At this point any package I install in this virtual environment will only be used when the environment is active.
There are a few more manual steps in the above process then I wanted, so I extended the shell script that Prabhu wrote to make this a simple one-command operation. One still needs to manually create each virtual environment, and install packages, but this script simplifies activating and deactivating them.
The venv_switch.sh script will:
- Activate the selected virtual environment. (Or issue an error if it doesn’t exist.)
- Launch a new bash shell using the ~/.virtualenvrc file which sources the virtualenv/activate script.
- The activate script modifies the PATH and prepends the bash prompt with the virtualenv label.
#!/bin/sh # venv_switch.sh # switch between different virtual environments # verify a virtualenv is passed in if [ $# -ne 1 ] then echo 'Usage: venv_switch venv-label' exit -1 fi # verify the virtualenv exists VENV_PATH=~/local/virtualenv/$1 # activate env script ACTIVATE_ENV=~/local/virtualenv/activate echo $VENV_PATH if [ -e $VENV_PATH ] then echo 'Switching to virtualenv' $VENV_PATH echo "Starting new bash shell. Simply 'exit' to return to previous shell" else echo 'Error: virtualenv' $VENV_PATH 'does not exist!' exit -1 fi rm $ACTIVATE_ENV ln -s ~/local/virtualenv/$1/bin/activate $ACTIVATE_ENV # Launch new terminal bash --rcfile ~/.virtualenvrc
Now to activate our numpy-1.1.1 virtual environment, we simply do:
To deactivate the virtual environment and go back to your original environment, just exit the bash shell:
The rcfile used to source the activate script. I first source my .profile to setup my environment and custom prompt, then source the virtual environment. .virtualenvrc:
# rc file to initialize bash environment for virtualenv sessions # first source the bash_profile source ~/.bash_profile # source the virtualenv source ~/local/virtualenv/activate
Set up an ets-3.0.0 virtualenv:
cburns@virtualenv 15:23:50 $ pwd /Users/cburns/local/virtualenv cburns@virtualenv 15:23:50 $ virtualenv ets-3.0.0 New python executable in ets-3.0.0/bin/python Installing setuptools............done. cburns@virtualenv 15:24:29 $ ls activate ets-3.0.0 numpy-1.1.1 numpy-1.2.0b2
Switch into my ets-3.0.0 virtualenv using the venv_switch.sh script:
cburns@~ 15:29:12 $ venv_switch.sh ets-3.0.0 /Users/cburns/local/virtualenv/ets-3.0.0 Switching to virtualenv /Users/cburns/local/virtualenv/ets-3.0.0 Starting new bash shell. Simply 'exit' to return to previous shell
Install ETS using easy_install. Note we need to use the easy_install from our ets-3.0.0 virtual environment:
(ets-3.0.0)cburns@~ 15:31:41 $ which easy_install /Users/cburns/local/virtualenv/ets-3.0.0/bin/easy_install (ets-3.0.0)cburns@~ 15:31:48 $ easy_install ETS