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July 30, 2021 08:51 pm GMT

Migrating a Super Simple CRUD App from Flask to FastAPI

What is FastAPI and Why Do I Need It?

Flask has been one of the more popular Python frameworks for many years, but its time for an update. Today, well be discussing Flasks faster, more efficient cousin: FastAPI. Compared to Flask, FastAPI is more performant and has Swagger documentation and other goodies built-in. If you want to run a Python web application in production in 2021, youll want to use FastAPI.

While there are some syntactical differences between how you write Flask and how you write FastAPI, youll find that theyre quite similar. Today were going to migrate a simple CRUD app from using Flask to Fast. So follow along!

Here is the original Flask code:

from flask import Flask, requestapp = Flask(__name__)@app.route('/basic_api/entities/<int:entity_id>', methods=['GET', 'PUT', 'DELETE'])def entity(entity_id):    if request.method == "GET":        return {            'id': entity_id,            'message': 'This endpoint should return the entity {} details'.format(entity_id),            'method': request.method        }    if request.method == "PUT":        return {            'id': entity_id,            'message': 'This endpoint should update the entity {}'.format(entity_id),            'method': request.method,            'body': request.json        }    if request.method == "DELETE":        return {            'id': entity_id,            'message': 'This endpoint should delete the entity {}'.format(entity_id),            'method': request.method        }

Now were going to break down each piece of this Flask code, and show you the equivalent code in FastAPI. First up, importing the libraries and instantiating the application object:

from flask import Flask, requestapp = Flask(__name__)from typing import Optionalfrom fastapi import FastAPIapp = FastAPI()

Next up, lets rewrite the /basic_api/entities/<int:entity_id> endpoint in FastAPI.

@app.route('/basic_api/entities/<int:entity_id>', methods=['GET', 'PUT', 'DELETE'])def entity(entity_id):   if request.method == "GET":       return {           'id': entity_id,           'message': 'This endpoint should return the entity {} details'.format(entity_id),           'method': request.method       }   if request.method == "PUT":       return {           'id': entity_id,           'message': 'This endpoint should update the entity {}'.format(entity_id),           'method': request.method,           'body': request.json       }   if request.method == "DELETE":       return {           'id': entity_id,           'message': 'This endpoint should delete the entity {}'.format(entity_id),           'method': request.method       }

Note that in FastAPI, the request methods are defined as methods on the FastAPI object, for instance @app.get, @app.put, @app.post, etc rather than as a parameter. Also note that instead of stating the type of the url parameter entity_id, within the route, its instead typed as a parameter in entity()

@app.get('/basic_api/entities/{entity_id}')def entity(entity_id: int):   return {       'id': entity_id,       'message': 'This endpoint should return the entity {} details'.format(entity_id),   }@app.put('/basic_api/entities/{entity_id}')def entity(entity_id: int, body: Entity):   return {       'id': entity_id,       'message': 'This endpoint should update the entity {}'.format(entity_id),       'body name': body.name   }@app.delete('/basic_api/entities/{entity_id}')def entity(entity_id: int):   return {       'id': entity_id,       'message': 'This endpoint should delete the entity {}'.format(entity_id),   }

Also note that in the put request route, we are passing along, as body, an Entity object. To define this object, we create a new class that inherits from BaseModel.

All together, the FastAPI application looks like:

from pydantic import BaseModelclass Entity(BaseModel):   name: str   description: Optional[str] = Nonefrom pydantic import BaseModelfrom typing import Optionalfrom fastapi import FastAPIapp = FastAPI()class Entity(BaseModel):   name: str   description: Optional[str] = [email protected]('/basic_api/entities/{entity_id}')def entity(entity_id: int):   return {       'id': entity_id,       'message': 'This endpoint should return the entity {} details'.format(entity_id),   }@app.put('/basic_api/entities/{entity_id}')def entity(entity_id: int, body: Entity):   return {       'id': entity_id,       'message': 'This endpoint should update the entity {}'.format(entity_id),       'body name': body.name   }@app.delete('/basic_api/entities/{entity_id}')def entity(entity_id: int):   return {       'id': entity_id,       'message': 'This endpoint should delete the entity {}'.format(entity_id),   }

And thats it! You can save the main.py file and run the server with

uvicorn main:app --reload

This will bring the server up on http://localhost:8000

One of the nice features of FastAPI is that it comes with Swagger already integrated. You can access it at http://localhost:8000/docs

From there, you can test each of your endpoints to see that they work!

Original Link: https://dev.to/e_farach/migrating-a-super-simple-crud-app-from-flask-to-fastapi-5ba7

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