title: Django: Help understanding a signal-function
body: <p>Good evening,</p>
  
  <p>I know, I asked a similar Question just a while ago, but I still got problems in understanding the more detailled functions of a signal. So I'm hoping someone can help me out with this one!? As an example I have a class in my "models.py" like this one:</p>
  
  <pre><code>class ExampleModel(models.Model):
      name = models.CharField(max_length=255, null=False, blank=False)
      value1 = models.IntegerField()
      value2 = models.IntegerField()
      value_of_1_and_2 = models.IntegerField()
  
      def __str__(self):
          return self.name
  </code></pre>
  
  <p>I would like to have my field "value_of_1_and_2" filled automatically with the sum of the other two fields before saving...
  Is this possible? I tried some things and got stuck with a "pre_save" like this:</p>
  
  <pre><code>@receiver(pre_save, sender=ExameplModel)
  def save(self, *args, **kwargs):
      ...
  </code></pre>
  
  <p>Thanks for all of your help and a nice evening to all of you!</p>