In addition to static and dynamic routes to functions/views using the @app.route() decorator, Flask empowers us with several powerful decorators to supplement the routes we create with .route(). In this article, we will look at some ways to run functions before and after a request in Flask using the decorators
- before_request
- after_request
before explaining those, let’s write a very basic flask application
from flask import Flask
app = Flask(\_\_name\_\_)
@app.route("/")
def index():
print("Index running!")
if \_\_name\_\_ == "\_\_main\_\_":
app.run()
So whenever a request to the root (“/”) is made, we would see the output shown below.
Index running!
We make use of before_request and after_requestIf we want any specific task to get executed before and after the request respectively.
before_request
The before_request decorator allows us to execute a function before any request. i.e, the function defined with the .before_request() decorator will execute before every request is made.
We can do this by decorating a function with @app.before_request:
@app.before\_request
def before\_request\_func():
print("before\_request executing!")
after adding this function, we get the following output whenever we try to make a request to the route (“/”).
before\_request executing!
Index running!
we can make use of this function in cases like :
- Opening database connections.
- tracking user actions
- adding a “back button” feature by remembering the last page the user visited before loading the next
- determining user permissions, etc……
before_request are not required to return anything, however, If a before_request function returns a value, it will be considered as if it was the return value for the view and any further request handling is stopped.
after_request
The after_request decorator works in the same way as before_request decorator, except, It allows us to execute a function after each request.
let us see an example by adding this function to our application:
@app.after\_request
def after\_request\_func(response):
print("after\_request executing!")
return response
by making a request to any route on our application we would see the following output:
before\_request executing!
Index running!
after\_request executing!
after_request functions must take and return an instance of the Flask response class.
this function can be used in cases like :
- close a database connection
- To alert the user with changes in the application, etc….
Any functions decorated with after_request will NOT run if the application throws an exception.
Our application :
from flask import Flask
app = Flask(\_\_name\_\_)
@app.before\_request
def before\_request\_func():
print("before\_request executing!")
@app.after\_request
def after\_request\_func(response):
print("after\_request executing!")
return response
@app.route("/")
def index():
print("Index running!")
if \_\_name\_\_ == "\_\_main\_\_":
app.run()
for more you can visit the flask documentation page here https://flask.palletsprojects.com/en/1.1.x/
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