Virtual environments can be described as isolated installation directories. This isolation allows you to localized the installation of your project’s dependencies, without forcing you to install them system-wide.
Imagine you have two applications, App1 and App2. Both use the package Pak, but require different versions. If you install Pak version 2.3 for App1, you would not be able to run App2 because it requires version 3.1.
This is where virtual environments come in handy.
Benefits:
- You can have multiple environments, with multiple sets of packages, without conflicts among them. This way, different projects’ requirements can be satisfied at the same time.
- You can easily release your project with its own dependent modules.
Here are two ways you can create Python virtual environments.
Virtualenv
[virtualenv](https://virtualenv.pypa.io/en/stable/) is a tool used to create isolated Python environments. It creates a folder which contains all the necessary executables to use the packages that a Python project would need.
You can install it with pip:
pip install virtualenv
Verify the installation with the following command:
virtualenv --version
Create an Environment
To create a virtual environment use:
virtualenv --no-site-packages my-env
This creates a folder in the current directory with the name of the environment (my-env/). This folder contains the directories for installing modules and Python executables.
You can also specify the Python version you want to work with. Just use the argument --python=/path/to/python/version. For instance, python2.7:
virtualenv --python=/usr/bin/python2.7 my-env
List Environments
You can list the available environments with:
lsvirtualenv
Activate an Environment
Before you can start using the environment you need to activate it:
source my-env/bin/activate
This ensures that only packages under my-env/ are used.
You will notice that the name of the environment is shown on the left of the prompt. This way you can see which is the active environment.
Install Packages
You can install packages one by one, or by setting a requirements.txt file for your project.
pip install some-package
pip install -r requirements.txt
If you want to create a requirements.txt file from the already installed packages, run the following command:
pip freeze > requirements.txt
The file will contain the list of all the packages installed in the current environment, and their respective versions. This will help you release your project with its own dependent modules.
Deactivate an Environment
If you are done working with the virtual environment you can deactivate it with:
deactivate
This puts you back to the system’s default Python interpreter with all its installed libraries.
Delete an Environment
Simply delete the environment folder.
Conda
Conda is a package, dependency and environment management for many languages, including Python.
To install Conda, follow these instructions.
Create an Environment
To create a virtual environment use:
conda create --name my-env
Conda will create the corresponding folder inside the Conda installation directory.
You can also specify which version of Python you want to work with:
conda create --name my-env python=3.6
List Environments
You can list all the available environments with:
conda info --envs
Activate an Environment
Before you can start using the environment you need to activate it:
source activate my-env
Install Packages
The same as with virtualenv.
Deactivate an Environment
If you are done working with the virtual environment you can deactivate it with:
source deactivate
Remove an Environment
If you want to remove an environment from Conda use:
conda remove --name my-env