Flask error handling skills

Flask is a popular Python web framework, and its flexibility and extensibility make it the preferred framework for many people. When developing web applications, you may encounter many problems, such as request errors, server errors, unhandled exceptions, etc. In this post, we’ll explore how to use Flask’s error handling techniques to handle these issues.

1. Application level error handling

In a Flask application, we can use the decorator @app.errorhandler() to handle the application level error. @app.errorhandler()Accepts a parameter indicating the type of error to be handled. For example, we can add the following code to the application to handle 500 errors:

@app.errorhandler(500)
def handle_500_error(error):
    return "Sorry, there was a server error.", 500

When a 500 error occurs in the application, Flask will call the handle_500_error() function to handle the error, and returns an HTTP response.

2. Blueprints level error handling

In Flask, Blueprint is an architecture that organizes view functions, templates and static files together. If we need to handle errors in a certain Blueprint, we can use the same trick, that is, use the errorhandler() decorator.

from flask import Blueprint, jsonify

bp = Blueprint('api', __name__, url_prefix='/api')

@bp.errorhandler(404)
def handle_404_error(error):
    return jsonify({'error': 'Not found'}), 404

In the above example, when some requests apply to Blueprint api, but the requested resource does not exist or is unavailable, Flask will call handle_404_error() Returns a 404 HTTP response.

3. Use abort() to handle errors

When we want to handle errors in the view function, we can use the abort() function to help We immediately abort the action, throw a specific error and return the specified error message.

from flask import abort

@app.route('/user/<id>')
def get_user(id):
    user = User.query.get(id)
    if not user:
        abort(404, description="User does not exist")
    return render_template('user.html', user=user)

In the above example, we check whether the user with the specified id exists. If not, the abort(404) function will throw a 404 error, abort the action, and return a 404 error page to the user. Custom error messages can be passed using the description parameter.

4. Custom error page

Finally, we can handle errors that occur during the request by customizing the error page. Flask provides a simple method to specify an error page:

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

In the above example, we defined a 404 error handling function to present the user with a specified 404.html page. In this page, you can add custom information, such as prompting the user that the page they are looking for does not exist, recommending some similar pages or websites, and providing links back to other pages, etc.

In Flask, error handling is a very important topic. By using the above tips, you can better handle request errors and provide a better user experience. So, please don’t ignore error handling!

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