django - Accessing admin model instance in form -

class productadmin(admin.modeladmin):     form = productadminform()  class productadminform(forms.modelform):      def __init__(self, request, *args, **kwargs):          super(productadminform, self).__init__(*args, **kwargs)          self.fields['field1'] = forms.charfield(required=false)          self.fields['field2'] = forms.integerfield() 

how can pass product instance productadmin productadminform? want provide different fields depending of products instances.

this:

class productadminform(forms.modelform):      class meta:          model = product       def __init__(self, *args, **kwargs):          super(productadminform, self).__init__(*args, **kwargs)               product_instance = self.instance              if product_instance.id , product_instance.myfield == "thatvalue":                  self.fields['field1'] = forms.charfield(required=false)                  self.fields['field2'] = forms.integerfield()