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04 - Foundations (Build Real Python Muscle)

Home: README

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

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

  1. Delete a required dict key and handle it safely.
  2. Change a numeric input to text and validate before math.
  3. 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.

Learning-style options (Play/Build/Dissect/Teach-back)

  • Play: mutate examples aggressively and observe behavior.
  • Build: complete every lab in order and commit after each lab.
  • Dissect: read a peer script and refactor it into smaller functions.
  • Teach-back: explain one lab weekly in writing or a recorded walkthrough.

Primary Sources

Optional Resources

Next

Next: concepts/how-loops-work.md →