["python","django","django-signals"]
django - comparing old and new field value before saving

I have a django model, and I need to compare old and new values of field BEFORE saving. I've tried the save() inheritance, and pre_save signal. It was triggered correctly, but I can't find the list of actually changed fields and can't compare old and new values. Is there a way? I need it for optimization of pre-save actions. Thank you!
There is very simple django way for doing it. "Memorise" the values in model init like this: def __init__(self, *args, **kwargs): super(MyClass, self).__init__(*args, **kwargs) self.initial_parametername = self.parametername --- self.initial_parameternameX = self.parameternameX Real life example: At class: def __init__(self, *args, **kwargs): super(MyClass, self).__init__(*args, **kwargs) self.__important_fields = ['target_type', 'target_id', 'target_object', 'number', 'chain', 'expiration_date'] for field in self.__important_fields: setattr(self, '__original_%s' % field, getattr(self, field)) def has_changed(self): for field in self.__important_fields: orig = '__original_%s' % field if getattr(self, orig) != getattr(self, field): return True return False And then in modelform save method: def save(self, force_insert=False, force_update=False, commit=True): # Prep the data obj = super(MyClassForm, self).save(commit=False) if obj.has_changed(): # If we're down with commitment, save this shit if commit: obj.save(force_insert=True) return obj Edit ( 06.05.2024 ): Please read through all the comments that have been added since I added this post 10 years ago. Things have changed, and though even I still use this approach myself and recommend using it, there are cases, where you need to tweak the approach or forgo using it. Again, read through the comments others have added.