[Flask] Flask redirection and errors

Flask redirects and errors

The Flask class has a redirect() function. When called, it returns a response object and redirects the user to another target location with the specified status code.

The prototype of the redirect() function is as follows:

Flask.redirect(location, statuscode, response)

In the above function:

The location parameter is the URL to which the response should be redirected.
The statuscode is sent to the browser header, the default is 302.
The response parameter is used to instantiate the response.

The following status codes have been standardized:

HTTP_300_MULTIPLE_CHOICES
HTTP_301_MOVED_PERMANENTLY
HTTP_302_FOUND
HTTP_303_SEE_OTHER
HTTP_304_NOT_MODIFIED
HTTP_305_USE_PROXY
HTTP_306_RESERVED
HTTP_307_TEMPORARY_REDIRECT

The default status code is 302 , which means'found' .

Flask class has abort() function with error code

Flask.abort(code)

The Code parameter takes one of the following values:

400 -for bad request
401 -for unauthenticated
403 - Forbidden
404 -not less than
406 -Indicates not to accept
415 -Used for unsupported media types
429 -Too many requests

Let us make a slight change to the login() function in the above code . If you want to display the'Unauthurized' page, replace it with a call to abort(401) instead of redisplaying the login page.

Create python file url_redirect.py

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

@app.route('/')
def index():
   return render_template('login.html')

@app.route('/login',methods = ['POST', 'GET'])
def login():
   if request.method == 'POST':
      if request.form['username'] == 'admin' :
         return redirect(url_for('success'))
      else:
         abort(401)
   else:
      return redirect(url_for('index'))

@app.route('/success')
def success():
   return 'logged in successfully'

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

Create a new template/login.html in the same level directory of the url_redirect.py file

<html>
   <body>

      <form action = "http://localhost:5000/login" method = "post">
         <p>Enter Name:</p>
         <p><input type = "text" name = "username" /></p>
         <p><input type = "submit" value = "submit" /></p>
      </form>

   </body>
</html>

Run the python file, then open the browser to visit http://127.0.0.1:5000/