Typed API Response

A unified, type-safe API response format for Python — with full type inference, Pydantic support, and consistent structure for both success and error responses. Just pass your data or exception — build_api_response() handles the rest.

Works seamlessly with FastAPI, Django Ninja, or any Pydantic-based Python project. Accepts Pydantic models, dataclasses, or any structured object.

🧪 Type Safety

This library is:

• Designed for Pylance and mypy strict mode
• Fully generic — type-safe through all layers
• Uses overloads to preserve type inference

No need to type hint manually:

response = build_api_response(data=MySchema(...), status=200)
# response.payload.data is inferred as MySchema ✅

➡️ Want proof? See the typecheck file

This is a static analysis file for mypy. It uses reveal_type() to confirm that generic types and payload structures are preserved correctly.
You can run it with mypy or open it in VSCode and hover to inspect types inline — no need to execute the file.

🔧 Features

• ✅ Typed response builders for both success and error responses
• ✅ Fully generic, Pylance-compliant with strict mode enabled
• ✅ Single unified function: build_api_response(...)
• ✅ Extensible metadata support via ResponseMeta
• ✅ Automatically distinguishes between data and error
• ✅ Raises clean custom exceptions on misconfiguration

🚀 Getting Started

Install with pip

pip install typed-api-response

Define your Pydantic response schema

from pydantic import BaseModel

class MyOutputSchema(BaseModel):
    product_name: str
    description: str
    price: float
    qty: int
    on_sale: bool

Create a typed API response:

@router.post("/foo")
def foo():
    your_data = MyOutputSchema(
      product_name="Big Bag of Rice",
      description="The world's greatest rice ever made. Anywhere. Ever.",
      price=17.99,
      qty=47328,
      on_sale=False,
    )
    response = build_api_response(data=your_data, status=200)
    # response.payload.data is inferred as MyOutputSchema ✅

✅ build_api_response() accepts any Pydantic model or well-typed object (e.g. a dataclass) and wraps it into a fully structured, metadata-rich response — with full type hint propagation and IDE support via generics.

Handling errors just as cleanly

You can also return exceptions using the same unified response format:

try:
    ...
except Exception as e:
    return build_api_response(error=e, status=418)

✅ build_api_response() wraps the exception in a type-safe, structured error payload — so your failure responses stay as consistent and predictable as your success ones.

🧱 API Structure

Unified Interface

def build_api_response(
    *,
    data: T | None = None,
    error: Exception | None = None,
    status: int,
    meta: ResponseMeta | None = None,
) -> ApiSuccessResponse[T] | ApiErrorResponse

• Provide either data or error, not both
• meta lets you attach timing, versioning, request ID, etc.
• If neither data nor error is passed, raises ApiResponseBuilderError

Success Response Format

{
  "status": 200,
  "meta": {
    "duration": null,
    "extra": null,
    "method": null,
    "path": null,
    "request_id": null,
    "timestamp": "2025-07-30T04:33:44.833Z",
    "version": null
  },
  "payload": {
    "success": true,
    "data": {
      "product_name": "Big Bag of Rice",
      "description": "The world's greatest rice ever made. Anywhere. Ever.",
      "price": 17.99,
      "qty": 47328,
      "on_sale": false
    },
    "error": null
  }
}

Error Response Format

{
  "status": 418,
  "meta": {
    "duration": null,
    "extra": null,
    "method": null,
    "path": null,
    "request_id": null,
    "timestamp": "2025-07-30T00:13:55.531Z",
    "version": null
  },
  "payload": {
    "success": false,
    "data": null,
    "error": {
      "type": "ZeroDivisionError",
      "msg": "division by zero"
    }
  }
}

🧠 Customizing Metadata

Use ResponseMeta to attach custom fields:

meta = ResponseMeta(
    request_id="abc123",
    version="v1.2.0",
    extra={"model": "en_streetninja", "debug": True}
)

return build_api_response(data=result, status=200, meta=meta)

🛡️ Exceptions

This package raises:

• ApiResponseBuilderError – if payload generation fails
• ApiPayloadBuilderError – if payload data is inconsistent or incomplete

📦 Components

• ApiResponseBuilder – abstract base class for builders
• ApiSuccessResponseBuilder – builds ApiSuccessResponse[T]
• ApiErrorResponseBuilder – builds ApiErrorResponse
• ResponseMeta – optional metadata block
• Payload / SuccessPayload[T] / ErrorPayload – structured payload schemas

☕ Support This Project

If this saved you time or made your API cleaner, feel free to buy me a coffee. Thanks for your support 🙏