          """
          Same behaviour as usual Field, except that we need to keep track
          of state so that we can deal with handling maximum depth.
          """
          super(BaseSerializer, self).initialize(parent)
          if parent.opts.depth:
              self.opts.depth = parent.opts.depth - 1
  
      #####
      # Methods to convert or revert from objects <--> primative representations.
 
</s> remove     def initialize(self, parent):
 </s> add     def initialize(self, parent, field_name): </s> remove     def initialize(self, parent):
 </s> add     def initialize(self, parent, field_name): </s> remove         self.fields = copy.deepcopy(self.base_fields)
 </s> add  </s> remove         self.read_only = self.default_read_only
 </s> add         self.read_only = kwargs.pop('read_only', self.default_read_only)

    def initialize(self, parent, field_name):
        super(RelatedField, self).initialize(parent, field_name)
        if self.queryset is None and not self.read_only:
            try:
                manager = getattr(self.parent.opts.model, self.source or field_name)
                if hasattr(manager, 'related'):  # Forward
                    self.queryset = manager.related.model._default_manager.all()
                else:  # Reverse
                    self.queryset = manager.field.rel.to._default_manager.all()
            except:
                raise
                msg = ('Serializer related fields must include a `queryset`' +
                       ' argument or set `read_only=True')
                raise Exception(msg)
        super(BaseSerializer, self).initialize(parent, field_name)
          """
          Same behaviour as usual Field, except that we need to keep track
          of state so that we can deal with handling maximum depth.
          """
        super(BaseSerializer, self).initialize(parent, field_name)
          if parent.opts.depth:
              self.opts.depth = parent.opts.depth - 1
  
      #####
      # Methods to convert or revert from objects <--> primative representations.
keep keep keep keep replace keep keep keep keep keep
 `queryset` argument is now optional on writable model fields. 
rest_framework/serializers.py