def formfield(self, **kwargs):
        from .widgets import BlobWidget
        from django.forms import FileField
        defaults = {'form_class': FileField, 'widget': BlobWidget}
        defaults.update(kwargs)
        return super(BlobField, self).formfield(**defaults)
A file widget is provided, but use model FileField or
dataset/ETHPy150Open django-nonrel/djangotoolbox/djangotoolbox/fields.py/BlobField.formfield