VirtualEnv Tutorial Overview

Virtualenv tutorial. In this tutorial I will show you in easy steps how to install and use VirtualEnv & VirtualEnvWrapper on your CentOS 6.x environment.

Install Python

1

yum install python

yum install python

test python by typing: “python” and you should see something similar to:

Install Easy_Install

yum install python-setuptools

Install PIP

METHOD A: RECOMMENDED : Using Easy_Install

easy_install install pip

that’s it!

METHOD B: You also can install PIP using yum but it’s not recommended.

yum install python-pip

Please note that name of the command is pyton-pip under RHEL and friends. I recommend that you add the following alias to your ~/.bashrc file, enter:

echo 'alias pip="/usr/bin/pip-python"' >> $HOME/.bashrc
. $HOME/.bashrc

Reload your startup file (e.g. source .zshrc) and you’re ready to go.

VirtualEnv Tutorial

VirtualEnv Tutorial can only start with installation….

Install VirtualEnv

The first step on our virtualenv tutorial is to Install VirtualEnv

pip install virtualenv

Basic commands

before we’ll continue to VirtualEnvWrapper lets play a liitle with VirtualEnv:

Create new Virtual Environment

virtualenv myenv

the above command will create a new ‘myenv’ directory and will install easy_install and pip to that directory.

virtualenv tutorial

Activate your new environment

Before you can install any Python module into your virtual environment you need to activate it using:

. bin/activate

virtualenv tutorial

you can see now the command display your virtualenv name in left of the bash shell inside brackets (myenv).

Install something

Maybe Django?

pip install django

You can see inside the myenv/lib/python2.6/site-packages you will find the django framework egg.

Use the pip list  command to see installed packages:

pip list

Requirement file (requirement.txt)

You can create a requirement file which will help you download & install all the necessary libraries when you deploy or git clone your application elsewhere later.

to create a requirements file from a virtualenv setup (freeze):

pip freeze -l > requirements.txt

-l = If in a virtualenv that has global access, do not output globally-installed packages.

 

installing from a requirements file:

pip install -r requirements.txt

Deactivate

to leave the virtual environment use the command:

deactivate

notice that you are not connected to (myenv) anymore.

Delete

To delete a virtual environment just delete its folder:

rm -rf myenv

 

VirtualEnvWrapper

we’ve finished with the virtualenv tutorial basics. so,… you want more?

virtualenvwrapper is a set of extensions to virtualenv. The extensions include wrappers for creating and deleting virtual environments and otherwise managing your development workflow, making it easier to work on more than one project at a time without introducing conflicts in their dependencies.

(Make sure you deactivated from your virtualenv before continue)

pip install virtualenvwrapper

Set up virtualenvwrapper

Virtualenvwrapper needs initialize it’s settings to work properly:

export WORKON_HOME=~/Envs
mkdir -p $WORKON_HOME
source /usr/local/bin/virtualenvwrapper.sh 

Notes:

• The default for WORKON_HOME is “.virtualenvs”. if you missing this line it will be set auto to default when running virtualenvwrapper.sh. I’ve changed it so you could see how it impacts.
• The third command creates new files inside your new ~/Envs (WORKON_HOME) folder.
  also, 
• You will want to add the command to source /usr/local/bin/virtualenvwrapper.sh to your shell startup file (~/bash_profile)

If the file virtualenvwrapper.sh is not there change the path depending on where it was installed by pip. whereis command can help you if you can’t find it:

whereis virtualenvwrapper.sh

…and that’s it! Now you’re all set to start using virtual environments!

Create First Environment

To create your first virtual environment type:

1

mkvirtualenv myenv

mkvirtualenv myenv

the command created a new ~/Envs/myenv folder with 4 folders inside (bin, include, lib and lib64 which is actually a symlink)

Note: as in Virtualenv. you can see that after the mkvirtualenv command you’ve entered the virtualenv automatically (myenv).

Exit

like in VirtualEnv – to exit virtual environment type:

deactivate

Workon

but now to work on your virtual environment again use:

workon myenv

you don’t need to cd into the folder and use the ./bin/activate command anymore. It’s working wherever you are on your filesystem.

The workon command also includes tab completion for the environment names.

 Using PIP with VirtualEnvWrapper

as in VirtualEnv – to install packages to local environment use (for Example Django):

pip install Django

We can see the new package with lssitepackages:

you can see the Django is here…

Requirements

you can also use the requirements.txt file you created earilier here (If you still have it) and use the

pip install -r requirements.txt

command to install all the packages here.

Delete

If you want to delete your environment just use:

 rmvirtualenv myenv

If you connected to this virtualenv you must deactivate first.

Customization scripts

When you type the workon command it invokes customization scripts as an environment is activated or deactivated (see Per-User Customization).

this simple example script from the readthedocs of VirtualEnvWrapper changes the folder for you when you workon:

(env1)$ echo 'cd $VIRTUAL_ENV' >> $WORKON_HOME/postactivate
(env1)$ workon env2
(env2)$ pwd
/Users/dhellmann/Envs/env2

or why not install something for us when we create a new virtual environment?

$ echo 'pip install sphinx' >> $WORKON_HOME/postmkvirtualenv

Project Manangement

If you want your project files to be in other location and your virtualenvs in other you can set the

export PROJECT_HOME=$HOME/MyProjects

and use the mkproject command to create both empty folder at your PROJECT_HOME and virtualenv at your WORKON_HOME

This is great feature! you don’t need to see the virtualenv folders at your project folder and you can save your requirment.txt file at the project.

Appendix: Virtualenv & Git

read this great script which helps you activate your virtualenv whenever you enter your git folder.

.Gitignore

For starter – you can find here a full python .gitignore for your new project.

Good luck!

+21

Etay Cohen-Solal

Development Specialist, Artist and Activist
Personal Website