Convert JSON Arrays to Python List Type Annotations

JSON Arrays to Python Lists

JSON arrays map to Python's list type. The element type is inferred from the array contents — strings become list[str], objects become list[SomeClass].

Primitive Arrays

{
  "tags": ["python", "json", "api"],
  "scores": [95, 87, 92],
  "weights": [0.5, 0.3, 0.2]
}

from dataclasses import dataclass

@dataclass
class Data:
    tags: list[str]
    scores: list[int]
    weights: list[float]

Object Arrays

{
  "users": [
    {"id": 1, "name": "Alice"},
    {"id": 2, "name": "Bob"}
  ]
}

@dataclass
class User:
    id: int
    name: str

@dataclass
class Root:
    users: list[User]

Empty Arrays

An empty JSON array [] is ambiguous — the converter cannot determine the element type. Most converters default to list[Any]. Once you know the expected type, update it manually:

from typing import Any

items: list[Any]  # converter default
items: list[str]  # manual fix after reviewing API docs

Nested Arrays

Arrays of arrays (e.g., a matrix [[1,2],[3,4]]) become nested list types:

matrix: list[list[int]]

Type Syntax Versions

Python version	Syntax
3.7-3.8	List[str] (from typing)
3.9+	list[str] (built-in)

The converter targets Python 3.9+ syntax by default, using lowercase list, dict, tuple, and set directly.

Iterating Typed Lists

for user in data.users:
    print(user.name)  # IDE knows user is User, provides autocompletion

Type-annotated lists give you proper autocompletion inside loops, comprehensions, and map/filter chains.