File Mimetype Validator

readme.md

This validator works well with FileField form fields and can validate that an uploaded file has an acceptable mimetype. Place this snippet in your app's validators.py.

Requirements:

This snippet uses python-magic. To install:

pip install python-magic

forms.py

from validators import MimetypeValidator

class MyForm(forms.Form):
    file = forms.FileField(
        allow_empty_file=False,
        validators=[MimetypeValidator('application/pdf')],
        help_text="Upload a PDF file"
    )

validators.py

from django.core.exceptions import ValidationError
import magic

class MimetypeValidator(object):
    def __init__(self, mimetypes):
        self.mimetypes = mimetypes
    
    def __call__(self, value):
        try:
            mime = magic.from_buffer(value.read(1024), mime=True)
            if not mime in self.mimetypes:
                raise ValidationError('%s is not an acceptable file type' % value)
        except AttributeError as e:
            raise ValidationError('This value could not be validated for file type' % value)