code: def full_name(self):
          
          if self.first_name and self.middle_name and self.last_name:
              return "%s %s %s" % (self.first_name, self.middle_name, self.last_name)
          if self.first_name and self.last_name:
              return "%s %s" % (self.first_name, self.last_name)
docs: Return the user's first name.