def __setitem__(self, key, value):
        self.clear_cache()
        self.payload[key] = value
Validates the POST data. If valid, displays the preview page.
dataset/ETHPy150Open dropbox/pynsot/pynsot/models.py/Resource.__setitem__--crossover with--dataset/ETHPy150Open django/django-formtools/formtools/preview.py/FormPreview.preview_post