Flask – URL Building

The url_for() function is very useful for dynamically building a URL for a specific function. The function accepts the name of a function as first argument, and one or more keyword arguments, each corresponding to the variable part of URL.

The following script demonstrates use of url_for() function.

from flask import Flask, redirect, url_for
app = Flask(__name__)

@app.route( /admin )
def hello_admin():
   return  Hello Admin 

@app.route( /guest/<guest> )
def hello_guest(guest):
   return  Hello %s as Guest  % guest

@app.route( /user/<name> )
def hello_user(name):
   if name == admin :
      return redirect(url_for( hello_admin ))
   else:
      return redirect(url_for( hello_guest ,guest = name))

if __name__ ==  __main__ :
   app.run(debug = True)

The above script has a function user(name) which accepts a value to its argument from the URL.

The User() function checks if an argument received matches ‘admin’ or not. If it matches, the apppcation is redirected to the hello_admin() function using url_for(), otherwise to the hello_guest() function passing the received argument as guest parameter to it.

Save the above code and run from Python shell.

Open the browser and enter URL as − http://localhost:5000/user/admin

The apppcation response in browser is −

Hello Admin

Enter the following URL in the browser − http://localhost:5000/user/mvl

The apppcation response now changes to −

Hello mvl as Guest