---
id: course-da-eda-l02
type: course
title: "Challenge 02: Define the answer first"
summary: "Sketch results.json — keys, types, rounding — before letting the agent write eda.py."
lang: en-US
content_version: 1
status: reviewed
reviewed_on: 2026-09-12
hints:
  - title: "What this checkpoint tests"
    body: "Defining the answer before generating it: sketch `results.json` — keys, types, rounding — before letting the agent write `eda.py`."
  - title: "Contract first"
    body: "Decide what `total_revenue` rounding means, what `revenue_by_region` keys look like, and that `rows_total` equals input rows — the suite compares exact numbers."
  - title: "When you are done"
    body: "Your sketch names every key in `results.json` and its source column."
---

# Challenge 02: Define the answer first

**Gate:** self-attested · **Points:** 10

Write down the shape of `results.json` before implementing anything:
which keys, which types, which rounding rules. The contract in `TASK.md`
defines the *form* — you decide what "correct" means for each value
before you let the agent generate code.

This is the anti-pattern this course exists to kill: "the agent wrote
code, it printed something, ship it." EDA only counts if the numbers are
*checkable*.

**Checkpoint:** you have a written list of the expected keys and you can
explain what each one means. Self-attested; record via
`python verify.py`.