2.0 What This Teaches
This tutorial covers the tools you need for Python development:
- Installing Python and verifying the installation
- Virtual environments for isolating project dependencies
- pip for installing and managing packages
- Project layout conventions
- IDE options for Python development
2.1 Installing Python
Download the latest Python 3 release from https://www.python.org. During installation on
Windows, check "Add Python to PATH" so you can run python from any terminal.
Verify the installation:
python --version
python3 --version
On macOS and Linux, the system may ship an older Python. Install a current version via
Homebrew (brew install python) or pyenv for managing multiple versions.
2.2 Virtual Environments
A virtual environment is an isolated copy of Python with its own package directory.
Installing packages into a venv keeps them separate from other projects and the system Python.
Always use a venv for real projects.
# Create a virtual environment in .venv/
python -m venv .venv
# Activate it (Linux/macOS)
source .venv/bin/activate
# Activate it (Windows PowerShell)
.venv\Scripts\Activate.ps1
# Your prompt changes to show (.venv)
# Now python and pip use the venv
# Deactivate when done
deactivate
The .venv folder is not committed to source control - add it to
.gitignore.
2.3 pip Package Manager
pip installs packages from PyPI (the Python Package Index at pypi.org).
With your venv active:
pip install requests # install a package
pip install requests==2.31.0 # install specific version
pip install -r requirements.txt # install from list
pip list # show installed packages
pip freeze > requirements.txt # save current packages to file
pip uninstall requests # remove a package
requirements.txt lists your project's dependencies so others can reproduce
your environment with pip install -r requirements.txt.
2.4 Project Layout
A minimal Python project looks like this:
my_project/
.venv/ # virtual environment (not in git)
src/
my_project/
__init__.py
main.py
tests/
test_main.py
requirements.txt
README.md
The __init__.py file marks a directory as a Python package.
It can be empty. The src/ layout prevents accidental imports from the
project root during testing.
2.5 pyproject.toml
Modern Python projects use pyproject.toml instead of setup.py.
It declares metadata and dependencies in a standard format:
[project]
name = "my_project"
version = "0.1.0"
requires-python = ">=3.11"
dependencies = [
"requests>=2.31",
]
Build tools like hatch, flit, or poetry read
this file. For simple scripts, requirements.txt is sufficient.
2.6 IDE Options
| IDE | Notes |
|---|
| VS Code + Python extension | Free, cross-platform, excellent venv integration, Pylance type checking |
| PyCharm Community | Free, Python-specific IDE with strong refactoring and debugging |
| Jupyter Notebook | Interactive notebook format; ideal for data exploration and teaching |
VS Code with the Python extension handles venv activation, debugging, and linting
automatically once you select an interpreter.
2.7 Exercise
Exercise
Create a new project folder called myapp. Create a virtual environment
in it. Activate it. Install the requests library. Capture the installed
packages to requirements.txt with pip freeze. Deactivate the
venv. Then recreate it fresh and verify you can restore packages from
requirements.txt.
2.8 Common Mistakes
Forgetting to activate the venv
Running pip install without activating the venv installs packages into
the system Python, not your project's venv. Your script then fails to import them
when run inside the venv. Always activate before installing or running.
Not pinning versions in requirements.txt
pip freeze captures exact versions (e.g., requests==2.31.0).
Writing only requests without a version means a different machine may
install a newer, incompatible version. Pin versions for reproducible builds.
Committing .venv to source control
The .venv folder is large, platform-specific, and regeneratable. Add
.venv/ to .gitignore. Teammates recreate it with
python -m venv .venv && pip install -r requirements.txt.
2.9 Key Terms
| Term | Meaning |
|---|
| venv | Virtual environment: isolated Python with its own packages |
| pip | Python package installer; installs from PyPI |
| PyPI | Python Package Index - the public package repository at pypi.org |
| requirements.txt | List of pinned package versions for reproducible installs |
| pyproject.toml | Modern project metadata and dependency declaration format |
| __init__.py | File that marks a directory as a Python package |
| interpreter | The python executable that reads and runs .py files |