Accessing self in class attribute

mixin.py

class A(object):
    
    # Dictionary
    extra_content = None
    
    def get_context_data(self, **kwargs):
        kwargs.update(extra_content)
        return kwargs
        
class B(A):
    extra_content = {
        'user': self.request.user, # This will fail
        'form': 'some form'
    }
    def get_context_data(self, **kwargs):
        """
        The kwargs below should have a 'user' & 'form' key.
        """
        kwargs = super(B, self).get_context_data(**kwargs)
        return kwargs
        
The thing is I can't access the self variable above.  I could change that to a string and use eval() to resolve it but
I'm wondering if there's a better solution.