Type annotation

2 snippets across 2 stacks — Python, TypeScript

PYPython

Type Hints / Annotations

syntax

name: type = value

example

price: float = 19.99
items: list[str] = ["apple", "bread"]
user_map: dict[str, int] = {"alice": 1}

output

# No runtime enforcement — hints are for tools and readers

Note Type hints do not prevent wrong types at runtime. Use mypy or pyright for static checking. Since 3.12, you can use the new type statement for aliases.

TSTypeScript

Variable Annotations

TS · Type Annotations

syntax

let varName: Type = value;
const varName: Type = value;

example

let orderId: string = "ORD-7821";
const maxRetries: number = 3;
let tags: string[] = ["urgent", "billing"];

// Often unnecessary when the type is obvious
let count = 0; // inferred as number
const label = "total"; // inferred as literal "total"

output

// Explicit annotations override inference when needed

Note Let TypeScript infer when the type is obvious from the initializer. Add explicit annotations when: the inferred type is too wide, you are declaring without initializing, or you want documentation clarity.