04 - Foundations (Build Real Python Muscle)¶

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Who this is for¶

Beginners who can run Python but still feel lost reading code.
Learners who need repeated, hands-on drills.

What you will build¶

A set of foundational scripts that solve small, real tasks.
A debugging notebook that captures mistakes and fixes.

Prerequisites¶

Setup complete from 03_SETUP_ALL_PLATFORMS.md.
Working .venv and pytest.

Step-by-step lab pack¶

Lab 1 - Inputs, outputs, and types¶

Goal: - Understand str, int, float, bool, and None.

Task: - Write a script that reads text values and converts them safely.

Minimum script behaviors: - Convert "42" to integer and add 10. - Reject invalid number text with a clear error message.

Lab 2 - Conditionals and decisions¶

Goal: - Build confidence with if, elif, else.

Task: - Evaluate an alert severity string and print an action: - Critical -> Page On-Call - Warning -> Create Ticket - else -> Log Only

Lab 3 - Loops and collections¶

Goal: - Process many records with predictable logic.

Task: - Iterate over a list of alert dictionaries. - Print a one-line summary for each. - Count critical alerts.

Lab 4 - Functions and reuse¶

Goal: - Break logic into testable units.

Task: - Implement: - normalize_status(text: str) -> str - is_critical(status: str) -> bool - Add pytest tests for both functions.

Lab 5 - Files and paths¶

Goal: - Read and write files safely with pathlib.

Task: - Read a text file of events. - Write a summary file containing counts by severity.

Lab 6 - Debugging drills¶

Goal: - Read tracebacks and isolate root cause quickly.

Task: - Trigger and fix: - KeyError - TypeError - FileNotFoundError

Record each incident in notes/debug_journal.md with: - error message, - root cause, - fix, - prevention rule.

Expected output¶

15+ micro-scripts in a dedicated foundations project.
20+ passing tests across key logic helpers.
Debug journal with repeated failure patterns and fixes.

Break/fix drills¶

Delete a required dict key and handle it safely.
Change a numeric input to text and validate before math.
Rename an input file and recover with clear error handling.

Troubleshooting¶

If loops confuse you: print intermediate values each iteration.
If functions confuse you: write expected input/output examples first.
If tests confuse you: test one function at a time with tiny data.

Mastery check¶

You are ready for the next phase when you can: - write and test small functions from scratch, - explain tracebacks in plain English, - process list-of-dict data without guesswork.