Srikanth Chekuri home

Flask cheat sheet

17 Nov 2019

Writing our own decorators in Flask. Below is the Flask minimal application code from documentation.

from flask import Flask
app = Flask(__name__)

def hello_world():
    return 'Hello, World!'

Flask uses decorators for its routing. @app.route('/') is the decorator in this minimal application. When writing apis we might want to protect some of our endpoints from anonymous users. If all of our endpoints are private we could use Flaskā€™s before_request to validate the request. When application has both public and private resource endpoints we need to ensure that no anonymous users get to access the private endpoints. This is the best use case to use python decorators with Flask.

import json
from functools import wraps

from Flask import Response

def api_access_required():
    def _api_access_required(func):
        def dec_function(*args, **kwargs):
            api_key = request.headers.get('api_key')
            valid_api_key = validate_api_key(api_key)
            if not valid_api_key:
                message = {
                    'message': 'You are not authorized to perform this action',
                    'status': 'failure',
                resp = Response(json.dumps(message))
                resp.status_code = 403
                return resp
            return func(*args, **kwargs)
        return dec_function
    return _api_access_required

Now we can import api_access_required and attach it to the any endpoint which needs a authorization for its resources.

from flask import Flask

import api_access_required from my_decorators

app = Flask(__name__)

def my_private_endpoint():
    return 'This is very secret message bois!'

We can also add arguments our custom decorator just like route which accepts string.