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Installing Python on Debian

Welcome to our tutorial guide on installing Python on Debian, one of the most stable and versatile Linux distributions. Python is a high-level, interpreted programming language known for its readability and simplicity, making it an excellent choice for beginners and experts alike. It's widely used in web development, data analysis, artificial intelligence, scientific computing, and more.

Before we dive into the installation process, let's understand why Python has become such a cornerstone in the programming world. Python's design philosophy emphasizes code readability with its notable use of significant whitespace. This means that the formatting of the code is part of the syntax, which often leads to more understandable code. It's like having a clean and organized workspace that helps you focus on the task at hand without the clutter.

As of writing, Python 3 is the latest major release of the language, and it's the version you should install. Python 2 has reached its end of life, and while it's still used in some legacy systems, all new projects should use Python 3.

Prerequisites​

  • A Debian-based system (e.g., Debian, Ubuntu, Linux Mint).
  • Access to a terminal window.
  • Basic knowledge of command-line operations.

Step 1: Update Package Lists​

First things first, let's make sure your package lists are up to date. This ensures that you're installing the latest available versions of Python and its associated packages.

sudo apt update

Here is our Output:. 

Hit:1 http://deb.debian.org/debian bullseye InRelease
Get:2 http://deb.debian.org/debian bullseye-updates InRelease [39.4 kB]
...
Fetched 6,649 kB in 7s (931 kB/s)
Reading package lists... Done

Step 2: Upgrade Existing Packages​

Next, upgrade the existing packages to their latest versions. This step is crucial to avoid any conflicts during the Python installation process.

sudo apt upgrade

You'll be prompted to confirm the upgrade. Press Y and Enter to proceed.

Step 3: Check Existing Python Installations​

Debian usually comes with Python pre-installed. Let's check which versions are already on your system.

python --version
python3 --version

The output for Python 2 (if installed):. 

Python 2.7.18

My output for Python 3:. 

Python 3.9.1

If Python 3 is already installed and the version is recent, you might not need to install it again. However, if you need a different version or if Python 3 is not installed, proceed to the next step.

Step 4: Install Python 3​

To install Python 3, along with the development headers and build utilities (which you'll need for compiling Python modules), run the following command:. 

sudo apt install python3 python3-dev python3-venv build-essential

This command installs Python 3, the development headers required for building new Python modules, the venv module for creating virtual environments, and the build-essential package which includes the GCC compiler and other essential tools for building software.

Step 5: Verify the Installation​

After the installation completes, verify it by running:. 

python3 --version

My output:. 

Python 3.9.1

You can also start the Python interpreter by typing:. 

python3

My output:. 

Python 3.9.1 (default, Jan  1 2021, 08:22:06) 
[GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

To exit the interpreter, type exit() and press Enter.

Step 6: Using Python Virtual Environments​

Virtual environments are a must for Python development. They allow you to manage dependencies for different projects separately. To create a virtual environment, run:. 

python3 -m venv myenv

Replace myenv with the name you want for your virtual environment. To activate the virtual environment, use:. 

source myenv/bin/activate

Your command prompt should now indicate that you are working inside the myenv virtual environment. To deactivate it, simply run:. 

deactivate

Step 7: Install Python Packages with pip​

pip is the package installer for Python. You can use it to install packages from the Python Package Index (PyPI). Ensure pip is installed for Python 3:. 

sudo apt install python3-pip

To install a package, for example, requests, inside your virtual environment, run:. 

pip install requests

What to Watch Out For​

  • Default Python Version: Ensure you're using Python 3 by explicitly calling python3 and pip3. Debian still includes Python 2 for legacy purposes, but it's best to use Python 3 for new projects.

  • Permissions: Some operations may require administrative privileges. Use sudo when necessary, but be cautious with permissions, especially when working with virtual environments.

  • Path Conflicts: Installing multiple versions of Python can lead to path conflicts. Use update-alternatives to manage which version of Python is used when python (without the version number) is called.

  • SSL Certificate Errors: If you encounter SSL certificate errors when using pip, you may need to update your Certificate Authority (CA) certificates:. 

    sudo apt install ca-certificates

You've successfully installed Python 3 on your Debian system and learned how to manage virtual environments and packages.

For further reading and resources, visit the official Python documentation. If you encounter any issues or have questions, the Debian and Python communities are excellent resources for troubleshooting and support.