flask_uploads.exceptions.UploadNotAllowed - Python

The flask_uploads.exceptions.UploadNotAllowed class is a built-in exception in the Flask-Uploads package, which is used for handling errors related to file upload attempts that fail due to incorrect file type, size or other restrictions.

Syntax

class UploadNotAllowed(Exception):
    pass

Parameters

This exception class does not have any specific parameters. It is used to signal that an upload attempt was not successful due to certain limitations set by the application or server.

Exceptions raised

The UploadNotAllowed exception is raised by the Flask-Uploads package when an attempt to upload a file does not meet certain upload constraints. This can include:

• File format: The package could be configured to only allow certain file extensions (e.g., .jpg, .gif, .png, .pdf) or MIME types (e.g., image/jpeg, audio/mp3)
• File size: The package could be configured to limit the maximum size of files that can be uploaded
• Upload frequency: The package could be configured to limit the number of uploads that can be made within a specific time frame

Example usage

Here is an example of how the UploadNotAllowed exception can be raised and handled in a Flask application:

from flask import Flask, request
from flask_uploads import UploadSet, IMAGES, configure_uploads
from flask_uploads.exceptions import UploadNotAllowed

app = Flask(__name__)
photos = UploadSet('photos', IMAGES)

app.config['UPLOADED_PHOTOS_DEST'] = 'static/images'
app.config['UPLOADED_PHOTOS_ALLOW'] = IMAGES
configure_uploads(app, photos)

@app.route('/upload', methods=['POST'])
def upload():
    try:
        photos.save(request.files['photo'])
    except UploadNotAllowed as e:
        return f"Upload not allowed: {str(e)}", 400
    return 'File uploaded successfully'

In this example, the upload() function attempts to save a photo submitted in a POST request to the static/images directory using the photos UploadSet instance. If the upload attempt fails due to a restriction set by the package (such as only allowing image files), an instance of the UploadNotAllowed exception is raised, and the error message is returned as the response with a 400 (Bad Request) status code.

Conclusion

The flask_uploads.exceptions.UploadNotAllowed class is an essential part of the Flask-Uploads library and helps application developers add file uploading capabilities to their Flask applications while enforcing certain restrictions to maintain security and compliance. By understanding the use cases and syntax of this exception class, developers can build more robust file upload features in their Flask applications.