Oct 01: Python Environment

Learning Objectives

After today's class, you should be able to:

Lesson Outline

Reading Debrief [10 min]

Week 6 reading (documentation mode)
- Which PostgreSQL types did you choose on Tuesday, and why?
- Which Faker providers did you find that fit your tables?
- Type hints: def make_hotels(count: int) -> list[tuple]:

Python venv [10 min]

Activate the environment you made for the class repository
- Linux/macOS: source .venv/bin/activate
- Windows (Git Bash): source .venv/Scripts/activate
- Your prompt should begin with (.venv)
What's inside .venv?
- which python and which pip – the copies inside .venv, not the system ones
- pip list – everything installed, including dependencies of dependencies
- pip show faker – the version, and where it came from
Why the versions in pyproject.toml are pinned
- Run pip install -e ".[dev]" again – Requirement already satisfied
- When a pin changes, that same command moves you to the new version
deactivate – and why import faker now fails

psycopg [10 min]

Same DB-API as sqlite3: connection, cursor, execute(), fetchall()
Differences: %s placeholders, connection string, with block closes the connection
Passwords belong in a password file, never in source code
Psycopg 3: Basic module usage

Faker [15 min]

Hotel database diagram

faker_demo_hotels.py
- GENERATED ALWAYS AS IDENTITY, and RETURNING to get the ids back
- Foreign keys come from those ids, not from range(1, 21)
- Faker.seed() – the same "random" data on every run

Lab Activity [30 min]