def connect(self, receiver, sender=None, weak=True, dispatch_uid=None):
        if isinstance(sender, six.string_types):
            try:
                app_label, model_name = sender.split('.')
            except __HOLE__:
                raise ValueError(
                    "Specified sender must either be a model or a "
                    "model name of the 'app_label.ModelName' form."
                )
            try:
                sender = apps.get_registered_model(app_label, model_name)
            except LookupError:
                ref = (app_label, model_name)
                refs = self.unresolved_references.setdefault(ref, [])
                refs.append((receiver, weak, dispatch_uid))
                return
        super(ModelSignal, self).connect(
            receiver, sender=sender, weak=weak, dispatch_uid=dispatch_uid
        )
dataset/ETHPy150Open django/django/django/db/models/signals.py/ModelSignal.connect