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Table of Contents
Python Virtual Environments
What and Why
A Virtual Environment is a tool to keep the dependencies required by different projects in separate places, by creating virtual Python environments for them. It solves the “Project X depends on version 1.x but, Project Y needs 4.x” dilemma, and keeps your global site-packages directory clean and manageable. For example, you can work on a project which requires Django 1.3 while also maintaining a project which requires Django 1.0. 1)
Using Virtual Environments
The python virtual environment package is installed by default on most CS machines. To make sure you can do the following:
user@computer:~/projects$ which virtualenv /usr/bin/virtualenv
Creating a new project
user@hester:~/projects$ virtualenv --no-site-packages exampleproject The --no-site-packages flag is deprecated; it is now the default behavior. New python executable in exampleproject/bin/python Installing distribute................................................................................done. Installing pip...............done.
user@computer:~/projects$ ls -l exampleproject/ total 4 drwxrwxr-x 2 user group 4096 Nov 25 10:16 bin drwxrwxr-x 2 user group 30 Nov 25 10:16 include drwxrwxr-x 3 user group 30 Nov 25 10:16 lib drwxrwxr-x 2 user group 56 Nov 25 10:16 local
user@computer:~/projects$ cd exampleproject/
Now you need to activate your virtual environment. This will setup some path variables to make the environments bin and lib directory to be the default.
user@computer:~/projects/exampleproject$ source bin/activate (exampleproject)user@computer:~/projects/exampleproject$
After activating the virtual environment you will notice that your prompt changed a little. This is not the only thing that has changed. Your $PATH and default python have changed as well (just checkout the bin/activate script to see what else it does).
Notice that the 'bin' directory in your virtual environment has been prepended to $PATH and the python and pip executables are inside the bin directory.
(exampleproject)user@computer:~/projects/exampleproject$ echo $PATH /home/user/projects/exampleproject/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
(exampleproject)user@computer:~/projects/exampleproject$ which python /home/user/projects/exampleproject/bin/python
(exampleproject)user@computer:~/projects/exampleproject$ which pip /home/user/projects/exampleproject/bin/pip
So to actually install your own python modules you can use 'pip' or 'easy_install' to do so:
(exampleproject)user@computer:~/projects/exampleproject$ pip install docopt Downloading/unpacking docopt Downloading docopt-0.6.2.tar.gz Running setup.py egg_info for package docopt Installing collected packages: docopt Running setup.py install for docopt Successfully installed docopt Cleaning up...
Notice where docopt was installed (~/projects/exampleproject/local/lib/python2.7/site-packages):
(exampleproject)user@computer:~/projects/exampleproject$ ls -l local/lib/python2.7/site-packages/docopt* -rw------- 1 user group 19946 Mar 8 23:12 local/lib/python2.7/site-packages/docopt.py -rw------- 1 user group 26140 Mar 8 23:12 local/lib/python2.7/site-packages/docopt.pyc local/lib/python2.7/site-packages/docopt-0.6.2-py2.7.egg-info: total 40 -rw------- 1 user group 1 Mar 8 23:12 dependency_links.txt -rw------- 1 user group 86 Mar 8 23:12 installed-files.txt -rw------- 1 user group 21525 Mar 8 23:12 PKG-INFO -rw------- 1 user group 651 Mar 8 23:12 SOURCES.txt -rw------- 1 user group 7 Mar 8 23:12 top_level.txt
To deactivate or stop working on your environment use the function that gets sourced when you activate your environment:
(exampleproject)user@computer:~/projects/exampleproject$ deactivate user@computer:~/projects/exampleproject$
virtualenvwrappers goal is to make virtualenv easier to use… sort of like when iTunes automatically organizes your iTunes library.
Create a virtual environment
This creates the exampleproject folder inside ~/Envs.
user@computer:~/$ mkvirtualenv venv
Work on a virtual environment
'virtualenvwrapper' provides tab-completion on environment names. It really helps when you have a lot of environments and have trouble remembering their names. 'workon' also deactivates whatever environment you are currently in, so you can quickly switch between environments.
user@computer:~/$ workon venv
Deactivating is still the same:
user@computer:~/$ rmvirtualenv venv
Other useful commands
lsvirtualenv List all of the environments. cdvirtualenv Navigate into the directory of the currently activated virtual environment, so you can browse its site-packages, for example. cdsitepackages Like the above, but directly into site-packages directory. lssitepackages Shows contents of site-packages directory.