How can I validate file uploads in WTForms?

How can I validate file uploads in WTForms?

You can use the FileField along with validators like FileRequired and FileAllowed to validate file uploads.

Can you show me an example of how to implement that?

Sure! Here's a simple example:

from flask_wtf import FlaskForm
from wtforms import FileField, SubmitField
from wtforms.validators import FileRequired, FileAllowed

class UploadForm(FlaskForm):
    file = FileField('Upload File', validators=[FileRequired(), FileAllowed(['jpg', 'png'], 'Images only!')])
    submit = SubmitField('Submit')

What happens if the file type is not allowed?

If the file type is not allowed, the form will not validate, and an error message will be displayed to the user.

Can I customize the error message?

Yes, you can customize the error message by passing a message parameter to the validator, like this:

FileAllowed(['jpg', 'png'], 'Only JPEG and PNG files are allowed!')