How does FastAPI support automatic API documentation generation?

FastAPI - Interview Questions

FastAPI supports automatic API documentation generation using the OpenAPI standard. OpenAPI is a specification for building and documenting APIs, and FastAPI leverages this specification to automatically generate interactive API documentation. Here's how FastAPI achieves automatic API documentation generation:

1. Pydantic Models : FastAPI uses Pydantic models to define request and response data structures. These models include type hints and validation rules, which serve as the basis for generating documentation.

from pydantic import BaseModel

class Item(BaseModel):
    name: str
    description: str = None
    price: float
    tax: float = None?

2. Route Decorators : FastAPI uses route decorators (@app.get, @app.post, etc.) to define API endpoints. These decorators include metadata such as route paths, parameter types, and response models, which are used for documentation generation.

from fastapi import FastAPI

app = FastAPI()

@app.post("/items/")
def create_item(item: Item):
    return item?

3. Automatic Documentation Generation : FastAPI automatically generates interactive API documentation based on the defined routes, request and response models, and other metadata. The generated documentation includes detailed information about each endpoint, including route paths, HTTP methods, request parameters, response models, and example usage.

4. Swagger UI and ReDoc : FastAPI provides built-in support for Swagger UI and ReDoc, which are popular tools for viewing and interacting with OpenAPI documentation. When you run your FastAPI application and navigate to /docs or /redoc endpoints in your browser, you will see the automatically generated API documentation.

5. OpenAPI Schema : FastAPI generates an OpenAPI schema (formerly known as Swagger schema) based on the defined routes and models. This schema is a machine-readable JSON document that describes the API endpoints, request and response models, and other details required for documentation.

Example :

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    description: str = None
    price: float
    tax: float = None

@app.post("/items/")
def create_item(item: Item):
    return item?

When you run this FastAPI application and navigate to http://localhost:8000/docs in your browser, you will see the automatically generated API documentation with interactive features for testing endpoints.