========== Virtualenv ========== Virtual Python Environment builder or virtualenv is a tool which will help you to install different versions of Python modules in a local directory using which you can develop and test your code without requiring to install everything systemwide. Installation ============ You can install virtualenv either from distro provided package or through pip. :: $ sudo yum install python-virtualenv Or :: $ sudo pip install virtualenv Usage ===== We will create a directory call *virtual* inside which we will have two different virtual environment. The following commands will create an env called virt1. :: $ cd virtual $ virtualenv virt1 New python executable in virt1/bin/python Installing setuptools............done. Installing pip...............done. Now we can activate the virt1 environment. :: $ source virt1/bin/activate (virt1)[user@host]$ The first part of the prompt is now the name of the virtual environment, it will help you identify which environment you are in when you have multiple environments. To deactivate the environment use *deactivate* command. :: (virt1)$ deactivate $ So, now we will install a Python module called redis. :: (virt1)$ pip install redis Downloading/unpacking redis Downloading redis-2.6.2.tar.gz Running setup.py egg_info for package redis Installing collected packages: redis Running setup.py install for redis Successfully installed redis Cleaning up... With the same way we can install a project called yolk, which tells us which of the modules are installed. :: (virt1)$ pip install yolk (virt1)$ yolk -l Python - 2.7.3 - active development (/usr/lib64/python2.7/lib-dynload) pip - 1.1 - active redis - 2.6.2 - active setuptools - 0.6c11 - active wsgiref - 0.1.2 - active development (/usr/lib64/python2.7) yolk - 0.4.3 - active Now we will create another virtual environment *virt2* where we will install the same redis module but an old 2.4 version of it. :: $ virtualenv virt2 New python executable in virt1/bin/python Installing setuptools............done. Installing pip...............done. $ source virt2/bin/activate (virt2)$ (virt2)$ pip install redis==2.4 Downloading/unpacking redis Downloading redis-2.4.0.tar.gz Running setup.py egg_info for package redis Installing collected packages: redis Running setup.py install for redis Successfully installed redis Cleaning up... (virt2)$ pip install yolk (virt2)$ yolk -l Python - 2.7.3 - active development (/usr/lib64/python2.7/lib-dynload) pip - 1.1 - active redis - 2.4.0 - active setuptools - 0.6c11 - active wsgiref - 0.1.2 - active development (/usr/lib64/python2.7) yolk - 0.4.3 - active As you can see, yolk says that in this envrionment we have redis 2.4 installed. This way you can have many different environments for all of your development needs. .. note:: Always remember to create virtualenvs while developing new applications. This will help you keep the system modules clean.