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Virtual Environments Guide
Borrowed from: http://docs.python-guide.org/en/latest/dev/virtualenvs/
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Virtual Environments
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.
virtualenv
virtualenv is a tool to create isolated Python environments. virtualenv creates a folder which contains all the necessary executables to use the packages that a Python project would need.
Install virtualenv via pip:
$ pip install virtualenv
Basic Usage
Create a virtual environment for a project:
$ cd my_project_folder
$ virtualenv venv
virtualenv venv will create a folder in the current directory which will contain the Python executable files, and a copy of the pip library which you can use to install other packages. The name of the virtual environment (in this case, it was venv) can be anything; omitting the name will place the files in the current directory instead.
This creates a copy of Python in whichever directory you ran the command in, placing it in a folder named venv.
You can also use a Python interpreter of your choice.
$ virtualenv -p /usr/bin/python2.7 venv
This will use the Python interpreter in /usr/bin/python2.7
To begin using the virtual environment, it needs to be activated:
$ source venv/bin/activate
The name of the current virtual environment will now appear on the left of the prompt (e.g. (venv)Your-Computer:your_project UserName$) to let you know that it’s active. From now on, any package that you install using pip will be placed in the venv folder, isolated from the global Python installation.
Install packages as usual, for example:
$ pip install requests
If you are done working in the virtual environment for the moment, you can deactivate it:
$ deactivate
This puts you back to the system’s default Python interpreter with all its installed libraries.
To delete a virtual environment, just delete its folder. (In this case, it would be rm -rf venv.)
After a while, though, you might end up with a lot of virtual environments littered across your system, and its possible you’ll forget their names or where they were placed.
Other Notes
Running virtualenv with the option --no-site-packages will not include the packages that are installed globally. This can be useful for keeping the package list clean in case it needs to be accessed later. [This is the default behavior for virtualenv 1.7 and later.]
In order to keep your environment consistent, it’s a good idea to “freeze” the current state of the environment packages. To do this, run
$ pip freeze > requirements.txt
This will create a requirements.txt file, which contains a simple list of all the packages in the current environment, and their respective versions. You can see the list of installed packages without the requirements format using “pip list”. Later it will be easier for a different developer (or you, if you need to re-create the environment) to install the same packages using the same versions:
$ pip install -r requirements.txt
This can help ensure consistency across installations, across deployments, and across developers.
Lastly, remember to exclude the virtual environment folder from source control by adding it to the ignore list.
virtualenvwrapper
virtualenvwrapper provides a set of commands which makes working with virtual environments much more pleasant. It also places all your virtual environments in one place.
To install (make sure virtualenv is already installed):
$ pip install virtualenvwrapper
$ export WORKON_HOME=~/Envs
$ source /usr/local/bin/virtualenvwrapper.sh
(Full virtualenvwrapper install instructions.)
For Windows, you can use the virtualenvwrapper-win.
To install (make sure virtualenv is already installed):
$ pip install virtualenvwrapper-win
In Windows, the default path for WORKON_HOME is %USERPROFILE%Envs
Basic Usage
Create a virtual environment:
$ mkvirtualenv venv
This creates the venv folder inside ~/Envs.
Work on a virtual environment:
$ workon venv
Alternatively, you can make a project, which creates the virtual environment, and also a project directory inside $PROJECT_HOME, which is cd -ed into when you workon myproject.
$ mkproject myproject
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.
Deactivating is still the same:
$ deactivate
To delete:
$ 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.
Full list of virtualenvwrapper commands.
virtualenv-burrito
With virtualenv-burrito, you can have a working virtualenv + virtualenvwrapper environment in a single command.
autoenv
When you cd into a directory containing a .env, autoenv automagically activates the environment.
Install it on Mac OS X using brew:
$ brew install autoenv
And on Linux:
$ git clone git://github.com/kennethreitz/autoenv.git ~/.autoenv
$ echo 'source ~/.autoenv/activate.sh' >> ~/.bashrc
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