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Virtual Environments |
Virtual Environments
Virtual environments can be described as isolated installation directories. This isolation allows you to localize the installation of your project's dependencies, without forcing you to install them system-wide.
Imagine you have two applications App1 and App2. Both require the package Pak, but each requires a different version. If you install Pak version 2.3 for App1, you would not be able to run App2, because it requires version 3.1. Here is when 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 three ways you can create Python virtual environments.
Tools used for creating Python virtual environments
Libraries
1. Virtualenv
virtualenv
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
You can list the available environments with:
ls virtualenv
Activate an Environment:
Note : On Windows, activating a virtual environment requires the user to have the permission to run scripts.
Before you can start using the environment you need to activate it:
For Mac OS or Linux systems :
source my-env/bin/activate
And for Windows:
.\my-env\Scripts\activate.bat
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.
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.
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.
To delete an Environment simply delete the environment folder.
2. venv
venv
is available by default in Python 3.3 and later.
To create a virtual environment use:
python3 -m venv venv
3. pyenv
pyenv
simple Python version management based on rbenv
.
Used together with pyenv-virtualenv
plugin
Create an Environemnt:
To create a virtual environment use:
pyenv virtualenv venv34
4. pyvenv
Deprecated in Python 3.6.
Dependency managers
1. Pipenv
Pipenv
manages dependencies on a per-project basis. It is like Node.js’ npm
or Ruby’s bundler
.
pipenv
automatically creates and track packges in your virtual environments. It combines pip
and virtualenv
together so you do need to use them separately.
You can install it with pip
:
pip install pipenv
Verify the installation with the following command:
pipenv --version
Create an Environment
To create a virtual environment, use pipenv
and specify which version of Python you want to use:
pipenv --python 3.6
Install Packages
Virtual environments created by pipenv do not need to be activated. Each project is managed independently. You simply go inside the project directory and install the packages you want:
pipenv install some-package
Pipenv will install the packge and create a Pipfile
inside the directory. The Pipfile tracks all packages and dependencies that your project needs. Pipfile
is the replacement of requirements.txt
when you use pipenv.
Uninstall Packages
To uninstall a package and remove it from Pipfile use:
pipenv uninstall some-package
If you want to uninstall all packages use:
pipenv uninstall --all
Import requirements.txt to Pipfile
You can import the packages and dependencies from requirements.txt
to your Pipfile using:
pipenv install -r requirements.txt
Executing Python Scripts
To run Python scripts use:
pipenv run python main.py
pipenv run
makes sure that packages installed with pipenv will be available to your program. You do not need to activate your virtual environment to do so.
Remove an Environment
If you want to remove the virtual environment from pipenv use:
pipenv --rm
You can also delete the environment by deleting the project directory.
Separate software stacks
1. Conda
Conda
is a package, dependency and environment management for many languages, including Python.
To install Conda, follow these instructions.
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
You can list all the available environments with:
conda info --envs
Before you can start using the environment you need to activate it:
source activate my-env
Install packages like with virtualenv
.
If you are done working with the virtual environment you can deactivate it with:
source deactivate
If you want to remove an environment from Conda use:
conda remove --name my-env
Additional Resources:
- Python Packaging Authority - Tool recommendations
- Python Packaging Authority - Creating Virtual Environments
virtualenv
official websitepipenv
official websiteConda
official websiteThe Hitchhicker's Guide to Python
- Pypenv & Virtual Environments