Installing Packages

Requirements for Installing Packages

This section describes the steps to follow before installing other Python packages.

Ensure you can run Python from the command line

Before you go any further, make sure you have Python and that the expected version is available from your command line. You can check this by running:

python3 --version

Note

Due to the way most Linux distributions are handling the Python 3 migration, Linux users using the system Python without creating a virtual environment first should replace the python command in this tutorial with python3 and the python -m pip command with python3 -m pip --user. Do not run any of the commands in this tutorial with sudo: if you get a permissions error, come back to the section on creating virtual environments, set one up, and then continue with the tutorial as written.

Create a virtual environment

python3 -m venv tutorial_env
source tutorial_env/bin/activate

This will create a new virtual environment in the tutorial_env subdirectory, and configure the current shell to use it as the default python environment.

Python “Virtual Environments” allow Python packages to be installed in an isolated location for a particular application, rather than being installed globally.

Imagine you have an application that needs version 1 of LibFoo, but another application requires version 2. How can you use both these applications? If you install everything into /usr/lib/python3.6/site-packages (or whatever your platform’s standard location is), it’s easy to end up in a situation where you unintentionally upgrade an application that shouldn’t be upgraded.

Or more generally, what if you want to install an application and leave it be? If an application works, any change in its libraries or the versions of those libraries can break the application.

Also, what if you can’t install packages into the global site-packages directory? For instance, on a shared host.

In all these cases, virtual environments can help you. They have their own installation directories and they don’t share libraries with other virtual environments.

Use pip for Installing

pip is the recommended installer. Below, we’ll cover the most common usage scenarios. For more detail, see the pip docs, which includes a complete Reference Guide.

pip install "SomeProject"

To install a specific version:

pip install "SomeProject==1.4"

To install a version that’s compatible with a certain version:

pip install "SomeProject~=1.4.2"

In this case, this means to install any version “==1.4.*” version that’s also “>=1.4.2”.

Upgrading packages

Upgrade an already installed SomeProject to the latest from PyPI.

pip install --upgrade SomeProject

Requirements files

Install a list of requirements specified in a Requirements File.

pip install -r requirements.txt

To write installed package to Requirements file:

pip freeze > requirements.txt