How can I handle file upload errors in WTForms?

How can I handle file upload errors in WTForms?

You can handle file upload errors in WTForms by using custom validators and error messages. Would you like an example?

Yes, please provide an example of a custom validator.

Sure! You can create a custom validator like this:

from wtforms import FileField, ValidationError

class FileRequired:
    def __call__(self, form, field):
        if not field.data:
            raise ValidationError('File upload is required.')

How do I integrate this validator into my form?

You can integrate it by adding it to your FileField like this:

class MyForm(FlaskForm):
    file = FileField('Upload File', validators=[FileRequired()])

What if the file type is not allowed?

You can add another custom validator to check the file type. Would you like to see how?