I'm using context from the model for 2 Many2one fields. Both link to the same model, but context should be different depending on a search result.

These are the relevant parts of the code:

class SomeModel(models.Model):
    _inherits = ...
    _name   = ...
    #...
    def _search_function(self):
        # some logic here

        return self.env['related.model'].search_read(...)[0]['id']
    # ...
    first_relational_field = fields.Many2one(  
           string="...",
           help="...", 
           comodel_name="other.model",
           domain="[('this_same_model_id','=',id)]",
           context="{'default_related_model_id': "+ str(self._search_function()) +"}",
            )

But the next error raises when upgrading the module:

...

context="{'default_price_version_id': "+ str(self._search_function()) +"}"

NameError: name 'self' is not defined

Why is self not available for the model?