Installation of Python

1.1 What Do You Need?

To start writing Python, you need:

1. Python 3 installed on your computer.
2. A terminal to run commands.
3. A text editor such as VS Code.

You can download Python from python.org.

1.2 Install Python on Windows

1. Open python.org/downloads.
2. Download the latest Python 3 installer for Windows.
3. Start the installer.
4. Select Add python.exe to PATH.
5. Select Install Now.

The PATH option allows you to run Python by typing python in a terminal.

Open PowerShell and check the installation:

python --version

You can also use the Windows Python launcher:

py --version

1.3 Install Python on Ubuntu or Debian

Open a terminal and run:

sudo apt update
sudo apt install python3 python3-pip python3-venv

Check the installation:

python3 --version
pip3 --version

1.4 Install Python on Fedora, RHEL, or CentOS

Run:

sudo dnf install python3 python3-pip

Then check the installation:

python3 --version

1.5 Install Python on macOS

Homebrew is a common way to install Python on macOS. If Homebrew is already installed, run:

brew install python

Check the installation:

python3 --version
pip3 --version

1.6 Verify That Python Works

Run a small Python command:

python3 -c "print('Python is working')"

On Windows, use python or py if python3 is not available:

python -c "print('Python is working')"

You should see:

Python is working

1.7 Write Your First Python File

Create a file named hello.py:

print("Hello, Python!")

Run it from the terminal:

python3 hello.py

On Windows, use:

python hello.py

The output should be:

Hello, Python!

1.8 Choose an Editor

You can write Python in any text editor, but these tools make learning easier:

• VS Code: A lightweight editor with Python support, debugging, and extensions.
• PyCharm: A full Python development environment.
• IDLE: A simple editor included with many Python installations.
• Jupyter Notebook: Useful for learning, experiments, and data analysis.

For this course, VS Code with the official Python extension is a good choice.

1.9 Create a Virtual Environment

A virtual environment keeps the packages for one project separate from other projects.

Create one inside your project folder:

python3 -m venv .venv

Activate it on Linux or macOS:

source .venv/bin/activate

Activate it on Windows PowerShell:

.venv\Scripts\Activate.ps1

After activation, your terminal usually shows (.venv). You can now install packages without affecting other projects.

To leave the virtual environment, run:

deactivate

1.10 Install a Python Package

pip is Python’s package installer. For example, install the requests package inside an activated virtual environment:

python -m pip install requests

Check that it works:

python -c "import requests; print(requests.__version__)"

Using python -m pip makes sure that pip belongs to the Python interpreter you are using.

1.11 What Happens When You Run Python?

When you run a Python file, Python reads the file and executes the instructions.

For now, you only need to remember this:

• You write Python code in a .py file.
• The Python interpreter runs the file.
• Python displays the result or an error message.

Python may create a __pycache__ folder while it runs. This folder contains temporary cached files. You normally do not need to edit it.

1.12 Basic Python Style

Python uses indentation to group code. Use four spaces for each indentation level.

name = "Alex"

if name:
  print(f"Hello, {name}")

Use clear names:

server_count = 3

Avoid unclear names:

x = 3

Python’s common style guide is called PEP 8. It helps teams write code that looks consistent and is easy to read.

1.13 Common Installation Problems

Python Command Not Found

This usually means Python is not installed or its directory is not in the PATH.

On Windows, reinstall Python and select Add python.exe to PATH. Then close and reopen PowerShell.

On Linux or macOS, try python3 instead of python.

The Wrong Python Version Appears

Several Python versions can exist on one computer. Check the version before installing packages or running a project:

python3 --version

On Windows:

py --list

pip Installs into the Wrong Python

Use this form instead of calling pip by itself:

python -m pip install package-name

PowerShell Does Not Allow Virtual Environment Activation

If PowerShell blocks the activation script, use Command Prompt, or ask an administrator to review the PowerShell execution policy for your machine. Do not change security settings without understanding your organization’s policy.

1.14 Practice Exercise

1. Install Python 3.
2. Confirm the Python version.
3. Create a file named system_check.py.
4. Add this code:

import platform

print(f"Operating system: {platform.system()}")
print(f"Python version: {platform.python_version()}")

5. Run the file from your terminal.

Interview Questions

• How do you check whether Python is installed?
• What is the difference between python, python3, and py?
• What is PATH, and why is it important?
• What is a virtual environment?
• Why should you use python -m pip?
• How do you run a Python file from the terminal?

Quick Interview Answer

To install Python, I install Python 3 from the official Python website or the operating system package manager. I verify it with python --version or python3 --version, create a virtual environment for each project, and install packages with python -m pip. On Windows, I make sure that Python is added to PATH during installation.

Key Takeaways

• Install Python 3, not Python 2.
• Always verify the installation from a terminal.
• Use a virtual environment for each project.
• Use python -m pip to install packages for the correct interpreter.
• Use VS Code or another editor to write Python files.

Chapter practice checkpoint

Run python --version (or python3 --version on systems using that command). Save print("Hello, automation!") in hello.py, then run it from the terminal with python hello.py.

Expected output: Hello, automation! on its own line.

Knowledge check: What is the difference between the interpreter prompt and a saved script?

You are ready to continue when you can locate your script, run it, change its message, and explain the output.