Abstract class for generic fields; in this case "created" and "modified".

models.py

# ...

class Base(models.Model):
    
    created = models.DateTimeField(_(u'Created'), editable=False)
    modified = models.DateTimeField(_(u'Modified'), editable=False)
    
    class Meta:
        abstract = True
    
    def save(self, *args, **kwargs):
        if not self.pk:
            self.created = datetime.datetime.now()
        self.modified = datetime.datetime.now()
        super(Base, self).save(*args, **kwargs)
    
    @property
    def is_modified(self):
        return self.modified > self.created

# ...

class Project(Base):
    
    # ...