Error Handling and Redirects in Flask

Flask provides useful error handling techniques and flexible redirect methods, which are crucial for web application development. This page covers how to use error handlers and redirects in Flask.

Syntax

Error Handlers:

@app.errorhandler(error_code)
def function_name(error):
    # code for handling the error

Redirects:

@app.route('/redirect-route')
def redirect_function():
    # code for processing the request
    return redirect(url_for('view_function', arg=value))

Example

Error Handlers:

from flask import Flask, render_template

app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, World!'

@app.errorhandler(404)
def page_not_found(error):
    return render_template('page_not_found.html'), 404

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

Redirects:

from flask import Flask, redirect, url_for

app = Flask(__name__)

@app.route('/')
def index():
    return 'Index Page'

@app.route('/hello')
def hello():
    return 'Hello, World!'

@app.route('/user/<username>')
def user_profile(username):
    # some processing code
    return redirect(url_for('index'))

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

Output

Error Handlers:

In the example above, if a request is made to a URL that does not exist, the page_not_found function will be called, and the template page_not_found.html will be displayed.

Redirects:

In the example above, when a user requests a URL like /user/JohnDoe, the user_profile function will process the request and redirect the user to the index function.

Explanation

Error Handlers:

In Flask, error handlers are functions that are executed when an error occurs. You can assign an error handler to a specific error code using the @app.errorhandler decorator. Flask supports many HTTP error codes including 404 page not found error, 500 internal server error, and more. When an error occurs, Flask calls the assigned error handler and returns the output generated by it.

Redirects:

Redirects are used to send the user to a different URL instead of the requested URL. Flask provides the redirect function for this purpose. Typically, redirects are used after some processing is done, and the user needs to be sent to a different page. This is done using the url_for function, which returns the URL associated with the specified function.

Use

Error Handlers:

Flask error handlers are useful for handling errors gracefully without displaying a generic error message.

Redirects:

Flask redirects are useful when you want to send the user to a different URL after performing some processing.

Important Points

• Error handlers are executed when an error occurs.
• Flask supports many HTTP error codes including 404 page not found error, 500 internal server error, and more.
• Redirects are used to send the user to a different URL instead of the requested URL.
• redirect function is used to perform the redirect.
• url_for function is used to generate the URL for the specific function.

Summary

Flask provides useful error handling techniques and flexible redirect methods, making it easy to build web applications. Error handlers allow you to handle errors gracefully without displaying a generic error message. Redirects allow you to send the user to a different URL after performing some processing.