Python Virtualenv Tutorial

The headaches of dependency management are common to developers. One errant update requires hours of research to correct.  Often multiple applications overlap on library dependency requirements.  This could cause two applications running in the same environment to require two version of the same library.  These type of conflicts could cause a number of issues both in development and production.Enter Virtualenv.  Virtualenv is a tool that creates dependency silos.  It allows you to deploy applications to a single environment with isolated dependencies. Docker employs a similar strategy at the OS level. Virtualenv segregates only at the Python and library level — that is, the environments Python executable and libraries are unique to that virtual environment.  So instead of using the libraries installed at the OS environment level, you can separate Python versions and libraries into siloed virtual environments.  This allows you to deploy multiple applications in the same OS environment with different versions of the same dependencies.

Install Virtualenv

The install of Virtualenv is straight forward. Using pip, you can execute the below command from the terminal.

Alternatively, if using Anaconda you will need to use the below terminal command instead.

Your terminal output should look similar to the below.

Create an Environment

Virtualenv has one main command. The below line executed from the terminal will create a new “silo” or virtual Python environment in the Tutorial directory.

You should get some terminal output like below after executing.

The virtualenv command will build a directory structure including a binary, library and include directory for the new virtual environment that was created.

/bin contains your executables most notably Python and pip.

The /lib and /include directories include supporting files for Python and the application to be developed.

Activate Virtualenv

The activation script updates your path so that you can utilize this virtual environment without the hassle of navigating to the directory. It makes it a bit easier to use, but could be skipped if you are a terminal ninja and don’t mind the key strokes.

In the /bin directory there is an activate BASH script. You can execute using the below.

If you will note from my fumbling below that I had to modify the permission of the file to execute. I used the CHMOD 700 activate command to update the permissions. You may also need to make this update prior to running the activate script.

Deactivate Virtualenv

To undo the environment variable changes that were made by activate run the following command from the terminal. This will revert your path changes like they never happened. It’s as simple as that.

Removing an Environment

Removing a virtual environment is as simple as rm. Simply type the following to remove the directory and recursively its contents.

Now What

Well, now you need to install your libraries and application in the new virtual environment.  Pip makes sourcing your libraries easy.

I won’t go into the subtleties of pip some of which can be found here, but I will demonstrate a single pip install.

 

The following command will open a Python interpreter command line.  I will import our new pandas library and check the version. Version 19 is my global pandas version, but as you see from the terminal output, the version used in our Tutorial virtual environement is 22.

This tutorial should get you started with Virtualenv.  I have added the link to the Virtualenv page that can assist with some in depth configuration using parameters and configuration settings that can be used in special circumstances.

References

https://virtualenv.pypa.io/en/stable