Lesson 12 of 55
15 mins readPython Index Signatures and Record
In Plain English
When you do not know all property keys ahead of time, index signatures and Record<K, V> allow you to type dictionary lookups and dynamic key-value structures safely.
Core Rules to Remember
Index Signatures: Syntax [key: string]: Value allows arbitrary string or number property keys.
Record<K, V>: Built-in utility type providing clean map typing over known key unions.
Live Interactive Example
Hit Run Code to see it liveIndex Signatures and Record Types
Python 3.12
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Output Console
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How it works: HeaderMap accepts any arbitrary string keys, while statusMessages enforces exact completeness across StatusCode.
Your Turn: Micro Challenge
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Micro Exercise
Create an Environment Variable Registry
- Use Record to define type EnvVars as a map from "PORT" | "HOST" | "NODE_ENV" to string.
- Create an env object of type EnvVars with PORT "3000", HOST "localhost", and NODE_ENV "development".
- Print HOST and PORT.
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Sandbox Output
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