def formfield(self, **kwargs):
        defaults = {'form_class': BlockField, 'block': self.stream_block}
        defaults.update(kwargs)
        return super(StreamField, self).formfield(**defaults)
Produce a ``CAST`` expression.
dataset/ETHPy150Open torchbox/wagtail/wagtail/wagtailcore/fields.py/StreamField.formfield--crossover with--dataset/ETHPy150Open goFrendiAsgard/kokoropy/kokoropy/packages/sqlalchemy/sql/elements.py/Cast.__init__