In the Python web development ecosystem, two frameworks have gained significant popularity: FastAPI and Flask. While both serve the purpose of building web applications and APIs, they each bring unique strengths to the table. This article will help you understand the key differences between these frameworks and guide you in choosing the right one for your next project.
Introduction
The choice of a web framework can significantly impact your development experience and application performance. Flask has been around since 2010 and is known for its simplicity and flexibility, while FastAPI, released in 2018, has quickly gained traction for its modern features and impressive performance. Let's dive deep into what makes each framework unique.
Key Differences
1. Performance and Async Support
FastAPI is built on top of Starlette and leverages Python's async capabilities out of the box. This makes it particularly well-suited for high-performance applications that need to handle multiple concurrent requests.
# FastAPI async example
from fastapi import FastAPI
app = FastAPI()
@app.get("/items/{item_id}")
async def read_item(item_id: int):
return {"item_id": item_id}
Flask, on the other hand, follows a synchronous approach by default, though async support can be added through extensions:
# Flask example
from flask import Flask
app = Flask(__name__)
@app.route("/items/<int:item_id>")
def read_item(item_id):
return {"item_id": item_id}
What this means is that FastAPI can handle more requests per second compared to Flask, especially in scenarios where async processing is crucial. However, Flask can be used together with wsgi servers like Gunicorn to achieve similar performance.
2. Type Hints and Validation
FastAPI shines when it comes to type hints and automatic validation:
# FastAPI with Pydantic models
from fastapi import FastAPI
from pydantic import BaseModel
class Item(BaseModel):
name: str
price: float
is_offer: bool = False
app = FastAPI()
@app.post("/items/")
async def create_item(item: Item):
return item
Flask requires additional libraries like Marshmallow for similar functionality:
# Flask with Marshmallow
from flask import Flask, request
from marshmallow import Schema, fields
app = Flask(__name__)
class ItemSchema(Schema):
name = fields.Str(required=True)
price = fields.Float(required=True)
is_offer = fields.Bool(default=False)
@app.route("/items/", methods=["POST"])
def create_item():
schema = ItemSchema()
item = schema.load(request.json)
return item
3. Documentation and OpenAPI Support
FastAPI automatically generates interactive API documentation using OpenAPI (Swagger) and ReDoc:
# FastAPI documentation is automatic
from fastapi import FastAPI
app = FastAPI(
title="My API",
description="This is a sample API",
version="1.0.0"
)
@app.get("/items/", tags=["items"])
async def list_items():
"""Retrieve a list of items.
Returns a list of all available items in the system.
"""
return [{"name": "Item 1"}, {"name": "Item 2"}]
Here's how the documentation looks in FastAPI:
Flask requires additional setup and extensions like flasgger for similar documentation:
# Flask with Flasgger
from flask import Flask
from flasgger import Swagger
app = Flask(__name__)
swagger = Swagger(app)
@app.route("/items/")
def list_items():
"""Retrieve a list of items
---
responses:
200:
description: A list of items
"""
return [{"name": "Item 1"}, {"name": "Item 2"}]
4. Ecosystem and Extensions
Flask has a mature ecosystem with a wide range of extensions for various functionalities, such as Flask-SQLAlchemy, Flask-RESTful, and Flask-SocketIO. FastAPI, being a newer framework, is rapidly growing its ecosystem but may have fewer extensions available compared to Flask.
Use-Case Comparison
FastAPI is an excellent choice for building high-performance APIs that require async capabilities, automatic validation, and interactive documentation. If you're starting a new project and performance is a top priority, FastAPI is a strong contender.
Flask, with its simplicity and flexibility, is well-suited for smaller projects, prototyping, and scenarios where async processing is not a critical requirement. It has a larger community and a vast number of extensions, making it a versatile choice for a wide range of applications.
Which Framework Should You Choose?
Choose FastAPI if:
You need high performance and async capabilities
- Type safety and automatic validation are priorities
- You want automatic API documentation
- You’re building a modern REST API
- You’re working on a new project with no legacy constraints
Choose Flask if:
You need high performance and async capabilities
- Type safety and automatic validation are priorities
- You want automatic API documentation
- You’re building a modern REST API
- You’re working on a new project with no legacy constraints