Week 5 (Blockchain track, Vyper): Guided build#

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Full context: root README, Week 5.

Goal#

A real Vyper contract, common failure modes at a conceptual level, and a first, still-scaffolded transaction sent from Python. Instructions are still fairly step-by-step.

Scope#

  • A Vyper contract beyond the trivial one from Week 4: state, access control, events.
  • Common failure modes at a conceptual level (reentrancy, overflow, access control), before writing anything complex, so security is a habit, not an afterthought.
  • With the contract deployed, send it a basic transaction and read its state back from a Python script, to confirm it actually works before automation enters the picture in Week 6.

The project: AssetRegistry#

Weeks 5, 6, and 7 build one project, not three. The contract you write and deploy this week, AssetRegistry, is the same contract the Week 6 backend service signs transactions against and the same contract the Week 7 service adds a second event handler and a test suite for. By the time you reach the Week 8 capstone, especially the acceptance gate, you will already have hands-on experience with exactly the shape of data that spec asks you to reason about: a holder's eligibility, a holder's balance (a size limit lives right next to it), and a timestamp of when that record last changed (a stand-in for "how fresh is the evidence backing this").

AssetRegistry is a deliberately small registry contract. It tracks, per address:

  • whether that address is a registered holder at all,
  • whether it is currently eligible to hold the asset,
  • its current balance, and
  • when that record was last touched.

Only the contract's owner (whoever deployed it, standing in for "our backend service") can register a holder or change any of those fields. Every change logs an event. That's the whole contract. It's small on purpose: the point of Weeks 5-7 is not "write a bigger contract," it's "build the off-chain muscle (transactions, managed keys, event handling, idempotency) that any real integration needs," and a small, well-understood contract is the right training weight for that.

This is the same contract, the same rules, the same fields, as the Solidity track's AssetRegistry. Only the language it's written in is different. If you've done the Solidity track already and are curious what changes and what doesn't, that's exactly what these notes walk through, but nothing here assumes you have.

Do this in order#

Steps 1-4 are required. Step 5 is optional; skipping it leaves no gap in what Week 6 assumes you know.

  1. notes/01-state-and-storage.md through 05-organizing-a-walkthrough-script.md, in order.
  2. exercises/00-guided-write-assetregistry.md, a line-by-line guided build of the contract's genuinely new pieces (struct, HashMap, the owner check), compiling after every step.
  3. exercises/01-read-and-predict.md, six short Vyper snippets to read and predict, two per failure mode.
  4. project/README.md's full walkthrough: deploy with Ape, export the ABI, run interact.py.
  5. Optional: exercises/02-guided-write-creditledger.md, a second, smaller guided build isolating just HashMap-plus-access-check, useful if that combination didn't fully click the first time; and project/README.md's two stretch goals (an aggregate read function, a fourth event) for more reps against this exact contract.