Python Install & Virtual Environment

Installing Python 3.12

1. Download Python 3.12 from python.org/downloads. Choose the installer for your operating system (Windows, macOS, or Linux).

2. Run the installer. On Windows, check Add python.exe to PATH before clicking Install.

3. Verify the installation by opening a terminal and running:

   python3 --version

   You should see Python 3.12.x. On Windows, use python --version instead.

   If Windows opens the Microsoft Store when you type python, the PATH was not set during installation. Re-run the installer, select Modify, and ensure the PATH checkbox is enabled.

Writing Your First Program

1. Create a new directory for your work:

   mkdir helloworld && cd helloworld

2. Create a file named app.py with the following content:

   print("Hello, World!")

3. Run it:

   python3 app.py

   On Windows use python app.py. You should see Hello, World! printed to the terminal.

Virtual Environments

A virtual environment isolates the Python packages for one project from those of another. Without it, installing a package for one project can break a different project that depends on a different version of the same package.

You will create a virtual environment in every project directory throughout this course.

Create and Activate

Use the built-in venv module to create an environment named venv at the root of your project:

python3 -m venv venv

Activate it before installing any packages:

• macOS / Linux:

  source venv/bin/activate

• Windows:

  venv\Scripts\activate

When activated, your terminal prompt shows the environment name (e.g., (venv)). All pip install commands now install into this isolated environment.

Install Packages

With the environment active, install packages normally:

pip install requests

Packages are stored inside the venv/ directory and do not affect your system Python or other projects.

Deactivate

When you are finished working:

deactivate

This returns you to the system Python. The installed packages remain inside venv/ for next time.

Best Practices

• Name the environment venv/ and add it to .gitignore so it is never committed to version control.

• Re-create the environment on a new machine by running python3 -m venv venv and then pip install -r requirements.txt (once you start tracking dependencies in a requirements file).

• Always activate the environment before running project code or installing packages.