title: Django AdminForm field default value
body: <p>I have a Django admin form.
  And now I want to fill it's initial field with data based on my model. So I tried this:</p>
  
  <pre><code>class OrderForm(forms.ModelForm):
      class Meta:
          model = Order
  
      email = CharField(initial="null", widget=Textarea(attrs={'rows': 30, 'cols': 100}))
  
      def __init__(self, *args, **kwargs):
  
          self.request = kwargs.pop('request', None)
  
          products = kwargs['instance'].products.all()
  
          self.message = purchase_message % (
              "".join(["&lt;li&gt;" + p.name + ": " + str(p.price) + "&lt;/li&gt;" for p in products]),
              reduce(lambda x, y:x + y.price, products, 0)
          )
  
          # and here I have a message in self.message variable
  
          super(OrderForm, self).__init__(*args, **kwargs)
  </code></pre>
  
  <p>At this point i don't know how to access email field to set it's initial value before widget is rendered. How can i do this?</p>