title: TypeError: unsupported operand type(s) for *: 'DeferredAttribute' and 'DeferredAttribute' django
body: <p>Good afternoon community,</p>
  <p>I am new to Django and in order to practice, I am building a financial website. The goal is that the user will insert data regarding company x, e.g. Apple, and the website will perform some metrics calculations to return to the user.</p>
  <p>I have two models so far:</p>
  <pre><code>class Company(models.Model):
  #Company data
  company_name = models.CharField(max_length=100)
  outstanding_shares = models.IntegerField()
  share_price = models.DecimalField(max_digits= 5, decimal_places=2)
  revenue = models.IntegerField()
  expenses = models.IntegerField()
  total_assets = models.IntegerField()
  total_liabilities = models.IntegerField()
  current_assets = models.IntegerField()
  current_liabilities = models.IntegerField()
  operating_cashflows = models.IntegerField()
  capex = models.IntegerField()
  
  #Date of creation
  created_at = models.DateTimeField(auto_now_add=True)
  updated_at = models.DateTimeField(auto_now= True)    
      
  def __str__(self):
      return self.company_name
  
  class Market_Cap(Company):          
  market_cap= Company.share_price * Company.outstanding_shares
  </code></pre>
  <p>When I run python manage.py check I get the following error:</p>
  <p>Market_Cap
  market_cap= Company.share_price * Company.outstanding_shares
  TypeError: unsupported operand type(s) for *: 'DeferredAttribute' and 'DeferredAttribute'</p>
  <p>Any hints as to how I can solve this problem?</p>
  <p>Thanks a lot in advance.</p>