Setting up a Python virtual environment in Linux using venv

When building a Python project, it’s good to sandbox your project so as to isolate the dependencies of the modules used. This is to avoid disrupting the system level Python installation.

Here we will be using venv to create the virtual environment in Linux. Do note that venv is a built in module in Python 3.3 and onwards.

1) Open terminal and navigate to the project folder.

Mine is py_nlp, for my Python NLP projects.

You can use ~ symbol if you are using Raspberry Pi as your Linux computer (like myself) and the project folder is in home/pi folder else you can key the whole path. Do take note that there is a space after cd.

$ cd ~/py_nlp


$ cd /home/pi/py_nlp

2. Create the virtual environment folder

We are using venv module which is only available from Python 3.3 onwards.

Now you are inside your project folder, key the following in terminal:

$ python3 -m venv venv

The top command means, using Py3 and module venv, create a venv folder for the virtual environment. You can use other name for the virtual environment but it’s a common practice to use venv (same name as module) for the folder name.

You can see that a folder, name venv, was created inside your project folder. And inside this venv folder, there are other folders, particularly ‘bin’ folder, which contains python interpreter files, pip files and some other files. Next we will call the ‘activate’ file (inside the bin folder), from the terminal to activate the virtual environment. You need to activate the virtual environment in order to use it.

3. Activate and deactivate the virtual environment(VE)

To develope within the VE, you need to activate it. Navigate to your project folder and In the terminal, key the following:

$ source venv/bin/activate

You will notice that your next line starts with ‘(venv)’, which means you are in the VE.

To deactivate or get out of the VE, just type :

(venv)…… $ deactivate

The (venv) disappear, which means you are out of VE. See below pic for the terminal screenshot.

The folders created within venv:

To add a module to the VE, like in this case I would like to add the nltk module to my NLP project, key ‘pip install nltk’. Remember you have to be inside the virtual environment (VE).

(venv) pi@raspberrypi:~/py_nlp $ pip install nltk

Keeping track of your virtual environment (VE) installed modules and their versions

Now that we have a virtual environment, we would like to keep track of the modules and their versions for a project. In your VE,

(venv) pi@raspberrypi:~/py_nlp $ pip freeze > requirements.txt

The above command will write all installed packages and their versions into the requirements.txt file. In this way you or another developer can know the versions and also next time if this project is move to a new VE or machine, you can just run the below script to installed the packages and their versions. Navigate to the directory containing the requirements.txt and key:

pip install -r requirements.txt