def add_extra_model_fields(sender, **kwargs):
    model_key = sender._meta.app_label, sender._meta.model_name
    for field_name, field in fields.get(model_key, {}):
        field.contribute_to_class(sender, field_name)
Injects custom fields onto the given sender model as defined
dataset/ETHPy150Open stephenmcd/mezzanine/mezzanine/boot/__init__.py/add_extra_model_fields