Day 1 – Python: Installation, Environments, and uv

Today's Focus

Install Python correctly, understand why virtual environments exist and how to use them, and get familiar with uv — the modern Python project manager that replaces pip and venv with a single fast tool.

Installing Python

Install Python via your OS package manager so it integrates with your system PATH and receives updates automatically. Avoid downloading installers from python.org — they create isolated copies that are harder to manage.

macOS (Homebrew):

brew install python
python3 --version
pip3 --version

Linux (apt):

sudo apt update && sudo apt install python3 python3-pip
python3 --version

Managing Multiple Python Versions

Different projects sometimes require different Python versions. pyenv lets you install and switch between them without affecting the system Python:

brew install pyenv           # macOS
# or: curl https://pyenv.run | bash   # Linux

pyenv install 3.12.0
pyenv install 3.11.8
pyenv global 3.12.0          # set the default
python3 --version

pyenv local 3.11.8           # pin a specific version for the current directory
cat .python-version          # pyenv reads this file automatically

Why Python Needs Virtual Environments

Python installs packages into a single global location shared by every project. This causes conflicts:

• Project A requires requests==2.28.0
• Project B requires requests==2.31.0
• Only one version can be installed globally at a time

A virtual environment is an isolated copy of Python and pip scoped to one directory. Packages installed inside it are invisible to everything outside.

Using venv (the built-in tool)

python3 -m venv .venv
source .venv/bin/activate       # macOS / Linux
# .venv\Scripts\activate        # Windows

pip install requests
pip list                        # only shows packages in this env

deactivate                      # leave the environment

You must source .venv/bin/activate in every new terminal session — there is no automatic activation.

Tracking dependencies with pip

pip install requests fastapi uvicorn
pip freeze > requirements.txt   # snapshot current packages
pip install -r requirements.txt # restore on another machine

The problem with pip freeze is that it captures every transitive dependency at whatever version happened to be installed. There is no proper lock file, and requirements.txt files drift over time.

uv — A Better Alternative

uv is a Python package and project manager written in Rust. It replaces pip, venv, and pip-tools with one tool that is significantly faster and more reliable.

Installing uv

curl -LsSf https://astral.sh/uv/install.sh | sh
source ~/.zshrc
uv --version

Starting a project with uv

mkdir ~/projects/hello-python && cd ~/projects/hello-python
uv init

This creates:

• pyproject.toml — project metadata and dependencies
• .python-version — the pinned Python version
• hello_python.py — a starter script
• uv.lock — the lock file (generated on first uv sync)

uv add requests          # installs and records in pyproject.toml
uv run python hello_python.py

uv run automatically creates and activates the virtual environment for that command. You never need to manually activate anything.

Writing and Running Python

Edit hello_python.py:

name = "Academy"
languages = ["Python", "JavaScript", "Go", "C#"]

print(f"Hello from {name}!")
print(f"This course covers: {', '.join(languages)}")

for i, lang in enumerate(languages, 1):
    print(f"  {i}. {lang}")

Run it:

uv run python hello_python.py

Tasks

• Install Python 3 via Homebrew or apt and verify with python3 --version.
• Install pyenv and use it to install two Python versions. Use pyenv local to pin one version in a test directory and confirm python3 --version reflects it.
• Create a project with python3 -m venv .venv, activate it, install a package with pip, run pip list, then deactivate and confirm the package is gone.
• Install uv. Create a new project with uv init, add a dependency, and run a script with uv run. Inspect pyproject.toml and uv.lock — note what each file contains.
• Write a Python script that prints a message using an f-string, loops over a list, and calls a function you define. Run it with uv run.

Reading / Reference

• uv documentation
• pyenv README
• Real Python: Python Virtual Environments primer
• Python packaging user guide