python-fastapi

Request Validation with FastAPI

Concept

This migrated snapshot demonstrates how FastAPI derives path, query, and request-body validation from Python type annotations and Pydantic models.

Hypothesis or problem

Typed endpoint signatures can keep validation rules close to HTTP handlers while generating an inspectable OpenAPI contract and interactive documentation.

Architecture

Boundary	Role
main.py	Defines typed models and endpoints for path, query, scalar body, embedded body, and multi-body validation.
requests.http	Exercises representative successful requests and generated documentation.
FastAPI and Pydantic	Convert annotations into runtime validation and OpenAPI metadata.

Quick path

Prerequisite: Python 3.11.

python -m venv .venv
.venv/bin/python -m pip install --requirement requirements.txt
.venv/bin/python -m uvicorn main:app
curl http://127.0.0.1:8000/hello/Forge

Open http://127.0.0.1:8000/docs or run the companion requests in requests.http to explore the validation cases.

Expected behavior

• Typed path and query parameters reject values outside their declared constraints with HTTP 422.
• Item bodies are parsed into Pydantic models and returned as JSON.
• PUT /itemsoptional/{item_id} accepts either an item body or no body.
• Multi-body and embedded-body endpoints demonstrate their distinct JSON shapes.

Tradeoffs

The repeated endpoint shapes favor tutorial visibility over application structure. Data is not persisted, several names are intentionally reused, and the historical FastAPI/Pydantic generation is pinned for snapshot fidelity rather than production use.

Status

Migrated snapshot from fronzec/fastapi-projects/tutorial at source commit 7a35799.

Verification

Verified on 2026-07-18 with Python 3.11.15:

• uv pip install --python <temporary-venv>/bin/python --requirement requirements.txt installed the pinned dependency set.
• uv pip check --python <temporary-venv>/bin/python reported that all installed packages are compatible.
• Compiling and importing main.py passed.
• Runtime smoke requests verified GET /hello/Forge, the bodyless optional-item update, and HTTP 422 for invalid constrained parameters.

Agent boundaries

Inherit the root AGENTS.md. Preserve the request-validation focus, avoid introducing persistence, and keep generated environments and response files out of the snapshot.