A beginner's guide to installing Python 3 and setting up a virtual environment
This guide covers how to install and upgrade Python 3 and how to create and an install into a Python virtual environment.
This is best practice in Python for both local and production code, as it isolates the scope where your python commands and pip commands run, protecting your global environment and allowing your to manage multiple virtual environments each with their own set of unique Python packages.
TL;DR
A summary of steps you'll learn about in this guide:
- How to install Python in macOS, Linux or Windows.
- Create virtual env.
$ python3 -m venv venv
- Activate virtual env.
$ # Linux/macOS $ source venv/bin/activate $ # Windows $ venv\Scripts\activate
- Install packages in the virtual env.
(venv) $ pip install package-name (venv) $ pip install -r requirements.txt
Table of Contents
If you already have Python installed, you can check the version you have. Or you'll get a message saying the command could not be found.
$ python --versionIf Python 2 is your system's default, you'll have to specify Python 3 instead.
$ python3 --versionIf you have a Unix-like system (Mac or Linux), you probably already have Python installed maybe not a new version of Python 3. Then skip to Upgrade Python below.
Follow instructions below to update the package manager then install the package.
For more detailed instructions or how to install for Windows or a Linux OS not listed below, I recommended reading this Real Python - Installing Python article. See also the Install Python 3 on a Mac article.
$ brew install python3Or more specifically, use a formula like python@3.9.
$ brew install python@3.9$ sudo apt-get update
$ sudo apt-get install python3From the Fedora Project article, which also covers using multiple Python versions and virtual environments.
$ sudo dnf install python39 # 3.9$ sudo yum update- From Real Python.
$ sudo yum install yum-utils $ sudo yum install https://centos7.iuscommunity.org/ius-release.rpm
- From the article on How to install Python3 on CentOS 7.
$ sudo yum install centos-release-scl $ sudo yum install rh-python39 # 3.9
From Real Python.
$ packman -S pythonProceed with caution. You may break your machine's environment (some programs may stop working), or make your existing virtual environments point to an inactive minor version of Python (this happened to me on a Mac).
$ brew upgrade python3$ sudo apt-get update && sudo apt-get upgrade python3Note that for Debian, the major versions are locked for a Debian version. Therefore you should upgrade to a newer Debian version to get a newer Python version. Or install it from a different repository or from source, but this is a custom installation which may be hard to get working or maintain, so I don't recommend it. For instance, when you install C headers or choose a Python version for your IDE, you system will not by default know to look in the custom location you've installed Python to.
How to create a virtual environment and install python packages into it. Only Unix-based systems are covered here.
Note that recent versions of Python 2 and 3 include pip already. And while the virtualenv library works for Python 2 and 3, I've read that venv is the recommended choice (it is actually a builtin for Python 3). So I use that here.
This guide uses Python's venv tool to manage virtual environments. When you create a virtual environment, it is setup to use a specific version of Python - you need to recreate it if you want to upgrade it.
Examples:
- Use system default for PY 3.
$ python3 -m venv <NEW_ENV_NAME>
- Specify target version, provided it is installed.
$ python3.7 -m venv <NEW_ENV_NAME> $ python3.6 -m venv <NEW_ENV_NAME>
- For any old projects where you really need use Python 2.
$ python2 -m venv <NEW_ENV_NAME>
Avoid using just python without a version number as you might get PY 2 or 3.
Note: The best tool for managing Python virtual environments is debateable. In short, virtualenv tool was popular but venv tool is supposed to be preferred over it. In fact, venv is now standard in Python3. Alternatives are pipenv and Virtual Env Wrapper.
Follow the steps below to add a virtual environment to your project directory under the name venv. With the first option that will be a directory and with the second option that will be a symbolic link to a uniquely name virtual environment in a chose central location.
The first option is simpler, however, it's is less maintainable since if you delete the project directory (or a repo), you'll also lose the venv. And if you move/rename the project, the links in the venv will break (though, there are special steps needed to make a venv directory relocatable).
Either way, make sure to update your project so the directory is excluded from version control.
.gitignore__pycache__/ venv
How to install a virtual environment in the same directory as your project or repo.
$ cd <PATH/TO/PROJECT>
$ python3 -m venv venvThat used the module flag to run the "venv" python module. It created a directory called "venv", though you could call it "virtualenv" or anything you like.
Instructions for Linux and macOS
Choose a location for install all your virtual envs across projects, then create symlinks (symbolic links to them as needed.
I've seen some people use the ~/.virtualenvs directory. However, this is already used sometimes such as if virtualenvwrapper is installed. I prefer to create a different directory that I saw recommended.
$ mkdir -p ~/.local/virtualenvs
$ cd ~/.local/virtualenvs
$ python3 -m venv my-project-name
$ cd <PATH/TO/PROJECT>Create soft (-s) symbolic link (ln) to the virtual environment directory. Note that if you move or the delete the directory, this link will no longer be valid.
$ ln -s ~/.local/virtualenvs/my-project-name venvCheck the symlink.
$ ls -l venv
lrwxr-xr-x 1 ... .... 47B 7 Feb 19:33 venv -> <USER_DIR>/.local/virtualenvs/my-project-name/If you ever need to point the symlink file to a different path, run this to delete and create the symlink. If you omit the force flag, you'll get an error that the file already exists.
$ ln -sf ~/.local/virtualenvs/my-project-name venvWithin the project directory, activate the environment. You'll need to do this each time you want to work on the project. Your IDE can be configured to recognize it for your automatically.
- Linux or macOS
$ source venv/bin/activate - Windows
> venv\Scripts\activate
Note how the prefix changed to show active status.
Upgrade pip.
$ pip install pip --upgradeInstall Python packages from project requirements file.
$ pip install -r requirements.txtInstall a Python package by name. Here are some examples.
$ pip install pandas
$ pip install requests==22.0.2Check to see how an activated virtual environment isolates your commands:
(venv) $ which python
<USER_DIR>/.local/virtualenvs/my-project-name/bin/python
(venv) $ which pip
<USER_DIR>/.local/virtualenvs/my-project-name/bin/pipUse deactivate to go back to your global environment and see your prompt change. But, install outside an virtual environment with caution, as conflicts can arise from different projects.
(venv) $ deactivate
$The reason this exists here as a gist is to make is easy to maintain a single set of Python setup instructions which I can link to from many projects. This can be embeded in Jekyll site using the jekyll-gist plugin and {% gist 3a4d14ba1763b4d6a1884f56a01412b7 %}.
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