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Setting up virtualenv
=====================
.. Contents::
Overview
--------
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_)
Installing
----------
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 virtualenv
----------------
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 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
Activate a virtualenv
---------------------
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
Install packages into a virtualenv
----------------------------------
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.
Pragmatic virtualenv
--------------------
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.
`venv_switch.sh`::
#!/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::
venv_switch.sh numpy-1.1.1
To deactivate the virtual environment and go back to your original
environment, just exit the bash shell::
exit
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
Installing ETS 3.0.0
--------------------
As another example, I installed ETS_ 3.0.0 for the Tutorial sessions
at Scipy2008_. (Note the prerequisites_.)
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
.. include:: ../../links_names.txt
.. _Prabhu: http://prabhuramachandran.blogspot.com/2008/03/using-virtualenv-under-linux.html
.. _Gael: http://gael-varoquaux.info/blog/
.. _Jarrod: http://jarrodmillman.blogspot.com/
.. _Fernando: http://fdoperez.blogspot.com/search/label/scipy
.. _Scipy2008: http://conference.scipy.org/
.. _prerequisites: https://svn.enthought.com/enthought/wiki/Install
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