Getting Started

Introduction

FastAPI is a modern, high-performance web framework for building APIs using Python. Designed with efficiency and developer productivity in mind, it takes full advantage of Python’s type hints to provide automatic validation, serialization, and robust error handling. FastAPI is particularly well-suited for building RESTful APIs, microservices, and backend services for real-time applications.

Core Features

• Asynchronous Programming
• Automatic Interactive API Documentation
• Type-Driven Development
• Data Validation with Pydantic
• Built-in Dependency Injection
• Security and Authentication

Tutorials

Official: FastAPI

PyImageSearch

• Getting Started with Python and FastAPI: A Complete Beginner’s Guide - PyImageSearch
• Deploying a Vision Transformer Deep Learning Model with FastAPI in Python - PyImageSearch
• Preparing FastAPI for Production: A Comprehensive Guide | by Raman Bazhanau | Medium

Getting Started

Installation

• Installs FastAPI, the framework we’ll use to build our APIs.
• Installs Uvicorn, the Asynchronous Server Gateway Interface (ASGI) that will run the FastAPI app and serve it to clients.
• Installs PyTest, a testing framework that allows us to write and run test cases for our FastAPI endpoints efficiently.

pip install fastapi uvicorn pytest

Verify the installation

python -m uvicorn --help

Running a Basic Server

main.py: (NOTE: 檔名不能與專案名相同，例如 fastapi.py)

from fastapi import FastAPI
app = FastAPI()
@app.get("/")
async def read_root():
    return {"message": "Hello, World!"}

Command to start the API Server

uvicorn main:app --reload

Access the Application : http://127.0.0.1:8000/ 

Example Code

Quick Test

from fastapi import FastAPI, File, UploadFile, HTTPException

app = FastAPI()

# http://127.0.0.1:8000/
@app.get("/")
async def read_root():
    return {"message": "Hello, World!"}

# http://127.0.0.1:8000/square?num=3
@app.get("/square")
async def calculate_square(num: int):
    return {"number": num, "square": num ** 2}

# http://127.0.0.1:8000/users/123
@app.get("/users/{user_id}")
async def read_user(user_id: int):
    return {"user_id": user_id}

Constraint/Validation

Pyantic: Base Constraint

from pydantic import BaseModel, Field

class User(BaseModel):
    name: str = Field(..., max_length=50)
    age: int = Field(..., gt=0, le=100)
    email: str = Field(..., regex="^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$")

Pyantic: Custom Error Messages

from pydantic import BaseModel, Field

class User(BaseModel):
    name: str = Field(..., max_length=50, description="Name must be under 50 characters")
    age: int = Field(..., gt=0, le=100, description="Age must be between 1 and 100")
    email: str = Field(..., regex="^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$", description="Invalid email format")

Pyantic: Combining Multiple Constraints

from pydantic import BaseModel, Field

class User(BaseModel):
    username: str = Field(..., min_length=3, max_length=20, regex="^[a-zA-Z0-9_.]+$")

Pyantic: Integration with FastAPI Endpoints

from fastapi import FastAPI, HTTPException
from pydantic import BaseModel, Field

app = FastAPI()

class User(BaseModel):
    name: str = Field(..., max_length=50)
    age: int = Field(..., gt=0, le=100)
    email: str = Field(..., regex="^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$")

@app.post("/user/")
async def create_user(user: User):
    return user