Lesson 10 of 12 · 32 min · Grades 9–12
Structured messages (JSON-shaped dicts)
IoT devices and web APIs speak JSON: nested dictionaries and lists. Even before import json, thinking in keys and lists is the skill. A telemetry packet is not a paragraph — it is a tree you walk with the same for and ["key"] you already have.
Telemetry packet
Nested keys like an API payload.
You will be able to
- ✓ Read nested keys
- ✓ Loop a list inside a record
Payloads are trees
packet["readings"] is a list. packet["device"] is a string. Walk with the tools you have. When you later call json.loads(text) in full Python, you get this exact structure.
Pretty-printing JSON is for humans. Programs should navigate keys, not slice characters of the raw text.
APIs and files speak this
A weather HTTP response, a WhatsApp export converted by a tool, a settings.json next to your app — all become dicts and lists. Advanced level will use requests.get(...).json() and get this tree. You already know how to walk it.
When a key is missing, decide: error (required field) or a default. Silent packet["temp"] that sometimes does not exist is how kiosks show blank screens.
Words that matter
- JSON
- A text format for nested objects and arrays; maps to dicts and lists in Python.
Common mistakes
Avoid: Parsing JSON with replace and split on commas.
Do this: Use the json module in real Python; here, use dicts directly.
Example program — One telemetry packet
Print each reading.
Edit the example, press Run, then Build if you want a compile check.
build
Press Build to compile.
Your turn — Campus node
A packet with device gate-1 must print gate-1.
Edit the example, press Run, then Build if you want a compile check.
build
Press Build to compile.
Self-assessment
Check your understanding before you mark the lesson complete.
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