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DAY 03 of 12

The language

Python — the backend's tool, from a first script to the standard library

You can do… by end of day
  • Write and run Python scripts: variables, data types, control flow, functions.
  • Debug a crashing script and fix it by reading the traceback.
  • Use the standard library workhorses: json, pathlib, csv, collections.
  • Build a small CLI tool and a data-processing script from a real file.
Deliverable

A small CLI tool + a CSV→JSON data script you can run on any machine.

Big-picture hook

You now write the glue that connects an app to its data. Next: make that glue talk HTTP and keep the data in one file.

Concepts what you'll understand
  • Python in a day: variables, strings, lists/dicts, conditionals, loops, functions — the core of the language.
  • Reading a traceback top-to-bottom and fixing the crash (not fear, a process).
  • json (the shape of almost every API), pathlib (files and folders without string surgery), csv (tabular data), collections (Counter, defaultdict).
  • F-strings, list comprehensions and the idioms that make Python read well.
The lab hands-on, ends with something live
  1. First script: a program that takes input and prints a result; then data types — turn one value into another.
  2. Fix the crash: a deliberately broken script — read the traceback, find the line, fix it, run it clean.
  3. CLI tool: a tiny command-line program (e.g. a word/line counter) that reads a file and prints a summary.
  4. Data processor: read a CSV, aggregate with collections.Counter, and write a JSON report.
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